JPS598318B2 - Wet gas scrubbing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing solid particulates and acid gases from gaseous mixtures.

In particular, the present invention relates to a method for removing solid particulates and acid gases from a gas mixture produced in a process for regenerating a catalyst used in the catalytic cracking of hydrocarbons.

The gaseous mixture produced in the regenerator of a fluid catalytic cracking process system contains solid particulates, including catalyst fines, and acid gases such as sulfur oxides.

It is desirable to reduce the levels of solid particulates and acid gases from such gases before releasing them into the atmosphere to minimize the harmful effects of these pollutants on ecology.

It is known that solid particles can be removed from the gas by a wet scrubbing process which involves scrubbing the gas with a jet ejector type venturi scraper where the scraping liquid enters the venturi via a spray nozzle under pressure.

The velocity of the liquid spray creates a draft in the chamber of the venturi scrubber, and the gas or vapor is directed across the body of the scrapper and through the narrow passages of the scrubber, where an intimate mixing of the scrubbing liquid and gas occurs. happens.

Generally speaking, the effluent of the scrubber (which may be one or more venturi structures in series or parallel) is sent to a separator where contaminated liquid is separated from the purge gas.

It is also known that acidic or basic substances can be added to the scrubbing liquid to neutralize or absorb basic or acidic contaminants that may be present in the gas undergoing the wet scrubbing process.

Although many types of Venturi-type wet gas scraping systems have been proposed to reduce the level of particulates and acid gases from gaseous mixtures before discharging them to the atmosphere, solid particulates and acid gases from gaseous mixtures are It has been found that the suitability of a particular wet scrubbing system for effective removal of other contaminants cannot be predicted.

Furthermore, it has been found that data obtained with one gas composition cannot necessarily be applied to other gas compositions.

Thus, the nature of the carrier gas, the nature and size of the solid particulate contaminants, and the nature of the contaminant gas are factors that influence the efficiency and operability of contaminant removal by any of the known Venturi wet gas scrubbing methods. It is.

According to the present invention, the gaseous mixture produced in the regenerator of a fluid catalytic cracking system contains solid particulate matter, including cracking catalysts consisting of submicron-sized particles, condensable contaminants, and sulfur oxides. It has been found that acid gases can be reduced to suitable levels by a wet gas scrubbing process carried out under certain conditions using a jet ejector venturi scrapper.

In accordance with the present invention, sulfur dioxide and cracking catalyst fines are removed from a gaseous effluent containing sulfur dioxide and cracking catalyst fines, the catalyst fines comprising up to about 40% by weight of particles less than 1 micron in size. (am) introducing the gaseous effluent into a venturi structure and introducing it into a venturi structure containing a basic material selected from the group consisting of alkali metal hydroxides, ammonium hydroxide, and ammonia; 7
(b) increasing the velocity of the mixture of gas and scrubbing mixture through the constricted passageway of the Venturi structure; , (C) recovering the mixture from step (b) from the venturi structure; and (d) separating said recovered mixture into a gaseous portion and a liquid portion having a reduced content of catalyst fines and sulfur oxides. A method for removing sulfur dioxide and cracking catalyst fines from a gaseous mixture comprising:

If desired, this gas portion can be reheated above its dew point before releasing it to the atmosphere.

In one embodiment of the invention, a portion of the liquid resulting from the separation step is recycled to the venturi structure as a scrubbing mixture.

Preferred embodiments of the invention will be described below with reference to the accompanying drawings.

The process of the invention is suitable for removing solid particulates and acid gases from gaseous effluents, particularly low pressure gaseous effluents, of refinery processes.

The method of the invention is particularly suitable for removing solid particulates and acid gases from gaseous mixtures produced in regenerators of catalytic cracking processes.

The solids in the gaseous mixture may contain up to 40% by weight submicron sized particles, typically from about 1 to about 40% by weight.

It is particularly suited for the treatment of gaseous mixtures produced in regenerators of fluid catalytic cracking process units.

Fluid catalytic cracking methods are well known (e.g. Hydroca
rbon Processing, 1 9 7 2
(September, pp. 131-138).

During the cracking reaction, carbonaceous materials deposit on the catalyst particles, thereby reducing their catalytic activity.

Therefore, it is common practice to circulate the stream of partially deactivated catalyst particles from the catalytic reaction zone to a regeneration zone where the carbonaceous deposits are burned off from the catalyst particles by combustion in the presence of an oxygen-containing gas such as air. This is the operation.

Regeneration can be carried out at temperatures within the range of 800 to below 1500°C.

When regeneration is carried out in the lower temperature range, ie, about 800-1300 DEG F., the regenerator gas effluent contains about 8-14 mole percent carbon monoxide (on a dry basis).

When it is desired to reduce the CO content of this gas, it is conventional practice to send the gas to a combustion zone, such as a CO boiler or furnace, thereby converting at least a portion of the CO to CO2.

When the regeneration process is carried out in the high temperature range, approximately 1300-1500° F., the regenerator gas effluent contains approximately zero to 12 mole percent as the initially formed CO is converted to CO2 in the high temperature regeneration. of CO.

In the latter case, regenerator gas is not normally passed to a CO boiler or furnace.

In many known methods, catalytic regeneration is performed at low pressure, e.g.
It is done below sig.

Therefore, the outlet pressure of the gaseous effluent of such a low pressure regenerator is also low.

Additionally, when the regenerator gas is combusted in a combustion vessel such as a CO boiler or furnace, the gas exiting the combustion vessel typically has a low pressure within the range of about -0.1 to 1.0 psig.

The gas purification method of the present invention can be applied to fluidized catalytic cracking regenerator gas obtained by low-temperature or high-temperature regeneration processes, which gas is optionally subsequently combusted in a combustion zone before being subjected to a wet scrubbing treatment. You may let them.

A typical composition of the regenerator effluent gas and the regenerator effluent gas that is later combusted in the CO boiler is as follows.

Regenerator gas components from the CO boiler Nitrogen 65-75 mol% Oxygen 1-5 mol% Carbon dioxide 10-15 mol% Water vapor 10-25 mol% Component Quantity Sulfur oxides 20-80 vppm
Nitrogen Oxides 50-200 vppm Solid Particulates 0.02-1.0 grains/SCF Regenerator Effluent Component Amount Nitrogen. Elements 60-70 mol% Oxygen <0.5 mol% Carbon dioxide 6-10 mol% Carbon monoxide 6-10 mol% Water vapor 10-30 mol% Sulfur oxides 20-800 vppm Nitrogen oxides
0-20 vppm solid particulates 0.
04~1.2 grains/SCF~ To explain the attached drawings, the gaseous effluent flows from fluid catalytic cracking regenerator 1 to line 1.
1 and introduced into a CO boiler 2 where it is combusted.

The combusted regenerator gas leaving the CO boiler is approximately -0.
0 φ psig pressure (this pressure ranges over a wide range from about -0.
1 to 1.0 psig) and about 60
0'F (this temperature may be in the range of about 200-1000'F).

The gaseous effluent of a CO boiler contains carbon dioxide, oxygen, sulfur dioxide, sulfur trioxide, nitrogen, condensables and solid particulates (which are primarily cracking catalyst fines used during the fluid catalytic cracking process). include.

Common catalysts used for cracking include siliceous materials such as silica, amorphous or crystalline (zeolite) silica alumina, silica zirconia, silica magnesia, and the like.

About 1-40% by weight of the catalyst particles in the gaseous effluent are less than 1 micron in size.

Condensable substances are components in the gaseous effluent (other than water vapor) that condense from the gaseous effluent as a solid or as a liquid under standard conditions of temperature and pressure, such as sulfates and H2S.
Any inorganic material such as O4 as well as organic material with hydrocarbon character.

The gaseous CO boiler effluent is taken off via line 13 and is sprayed with water introduced via line 27 for cooling.

The water-treated gas (now at a temperature of about 155'F) is introduced via line 15 to Venturi scrapper 3, where it is directed in line 23 to Venturi scrapper 3. It is injected into contact with a stream of aqueous scrubbing mixture.

In this case, no intermediate compression takes place between the CO boiler and the venturi scrubber.

The water treated gas is introduced into the Venturi scrubber at a rate of about 20-80 ft/sec, preferably about 40-50 ft/sec.

The scrubbing mixture is a scrubbing mixture 20~
Ratio of 120 gallons to 1000 ft" of gas, preferably 40-80 gallons of scrubbing mixture to 1 ft. of gas.
It is introduced into the venturi scrubber at a ratio of 000 ft3.

The scrubbing mixture is also introduced into the venturi scrubber at a temperature that is cooler than the temperature of the incoming water treated gas to assist in the desired entrapment of solid particles in the water.

Desirably, the scrubbing mixture injected into the venturi scrubber is about 5 to 50'F cooler, preferably about 10F cooler than the incoming water treated gas.

The scrubbing mixture is preferably about 6 to 7.
It is essential that the pH is maintained within a range of 7 or less.

Accurate control of pH determines the extent of sulfur oxides removed from the gas and affects the operability of the system, especially when implemented as a continuous operation of industrial equipment.

The pH is 7 to minimize unwanted CO2 absorption.
shall be maintained at no higher than.

A basic substance is added to the aqueous scrubbing mixture to control the pH.

The basic substance may be, for example, an alkali metal hydroxide, ammonia or ammonium hydroxide.

In a preferred embodiment of the invention, sodium hydroxide is used as the basic material for pH control of the scrubbing mixture.

Contact of the scrubbing mixture with the incoming gaseous mixture removes sulfur oxides from the gas by reaction with basic substances.

The scrubbed gas and scrubbing mixture flow through the constricted channels of the venturi scrubber, which increases the velocity of the mixture of gas and scrubbing mixture and cools the water over the solid particles in the usual manner. Condense.

The entire effluent of the venturi scrubber, ie at least a portion of the mixture of gas and liquid, is removed from the venturi scrubber via line 17 and is present at the bottom of the separator drum 4. Any liquid that may be present is introduced into the separator drum 4 above the V-bell (indicated by L in the accompanying drawings).

The pressure drop of the gas between the outlet pressure from the CO boiler and the outlet pressure from the separation vessel must be maintained at less than about 1 foot of water column and preferably less than about 2 inches of water column.

This is because the gas entering the venturi scrubber is a low pressure gas.

The method of the present invention eliminates the need to use a gas compressor in the system to move gas from the scrubber through the separation vessel to the chimney.

In the separator drum, the non-condensable gas portion of the venturi scrubber effluent is preheated above its dew point before flowing upwardly and discharging it to the atmosphere via the chimney 19.

Preferably, the preheating increases the temperature of the gas portion to about 5-75'F.
and preferably raises its temperature by about 30 degrees Fahrenheit, and can be accomplished by injecting hot gas into the upstream stream of purge gas via line 35.

The hot gas may be the effluent of the gas heater 5 into which fuel gas is introduced via line 31 and air is introduced via line 33.

The contaminated liquid scrubbing mixture forms a liquid phase at the bottom of the separator drum 4 (liquid hold-up zone).

This contains suspended solids (catalyst) and dissolved solids such as sodium sulfate, sodium sulfite, ammonium sulfate, and condensable liquid contaminants such as H2SO4.

Make-up water can be introduced into the liquid hold-up zone of the separator drum via line 25.

The liquid hold-up zone of the separator drum also includes a basic material (approximately 3
It is also possible to introduce sodium hydroxide at 0°Be'.

At least a portion of the liquid portion present in the separator drum is drawn off via line 21.

If desired, at least a portion of said liquid effluent, cooled to the desired temperature by conventional means such as a heat exchanger (not shown), is recycled to the venturi scrapper 3 via line 23 as a scrubbing mixture. .

Alternatively, make-up sodium hydroxide could be added to the recirculation line instead of or in addition to being introduced into the separator drum.

Another portion of the separator drum liquid effluent is removed from the process and, if desired, subjected to further processing such as concentration, solids removal and wastewater treatment to make it suitable for dumping. can be administered.

The following examples are provided to illustrate the method of the invention.

Example 1 To illustrate the efficiency of the process of the present invention for removing catalytic cracking catalyst fines and condensable substances such as H2SO4 and (NH4)zs04 from the gaseous effluent of a catalytic cracking catalyst regenerator, fluid catalytic cracking was carried out. The gas generated in the regenerator of the process equipment was scraped with a jet ejector type Venturi scrapper.

The specific venturi scrubber used in the test was
The scrubber was a model 7010 jet ejector type scrubber manufactured by Koertrol Corporation.

This type of scrubber requires a large amount of high pressure (40-120 psig) water flow to scrub and compress the gas stream.

Sodium hydroxide was used to control the pH of the aqueous scrubbing mixture.

The operating conditions and results for treating a 1000-3000 actual cubic foot per minute (ACFM) regenerator gaseous effluent are summarized in Table 1.

In a series of experiments summarized in Table 1, gas was introduced into a jet ejector venturi without pretreatment with water.

Table 1 Experiment ABCDEFG inflow gas velocity, ACFM 1830 1480 141
0 1040 2050 2230 2720
Inlet temperature, 'F 750 7
35 700 620 765 NA
NA effluent temperature, 'F 110
110 109 105 119
110 117 Triangular head, water column in
1.7 1.3 2.8 N
A NA NA 2-0 scrubber ``7g mixture speed'' 56 55 53
53 52 58 58gp
m Scragging mixture pressure' 56 56
52 52 50 90
90 psig Scrap 7/< -”% of 7 Scraps””” NA
92 98 94 104
80 80 mixture, lower scrubber ``Ichiriki'') ``Kura'': / 112
106 110 106 123
NA NA Bing Mixture, T Scrubbing Mixture pH 5.6
5.0 6.2 7.5 6.0
8.1 8.1 Amount of catalyst, grain/SCF inlet 0.264 0
．． 264 0.279 0.279 0.6
07 NA O. 246 exit
0.005 0.011 0.004
0.006 0.005 0.005 0.0
26 efficiency 98.2 95
．． 8 98.3 97.8 99.2
- - 89.3 Condensate volume, grain/SCF inlet 0.202 0.
202 0.124 0.124 0.352
0.269 0.056 exit
0.018 0.025 0.013 0
．． 010 0.007 0.004 0.003
Efficiency 91.2 87.8
89.6 92.3 98.0 9
8.5 94.9 NA Manual ACFM - Actual ft''/min SCF - Standard ft3 GPM - Gallons/min In these experiments, no attempt was made to measure S02 removal efficiency.

In experiments C and E, the pH was maintained within the pH range of the invention.

Example 2 In another set of experiments, gas produced in the regeneration vessel of a fluid catalytic cracking process unit was combusted in a CO boiler.

Thereafter, the gas stream exiting the CO boiler was scrubbed with a jet ejector venturi scrubber.

The specific Venturi scrubber used in these experiments was manufactured by ioinKoertrol Corporation.
It was a model #7010 jet ejector type scrubber manufactured by N.

Sodium hydroxide was used to control the pH of the aqueous scrubbing mixture.

Since CO boilers operate with limited backpressure, the scrubber's ability to compress low pressure gas eliminates the need for a blower or fan in the system.

The operating conditions and results are summarized in Table 2.

In this set of experiments, the gas was cooled in contact with water before introducing it into the jet ejector-type hentschuri.

Table 2 Experiment HIJKLMNOP Q Gas velocity, 767 810 880
890 897 855 750 753
700 635ACFM, scrapper population (10"°) Inflow of quenching zone 154 175 177 1
73 188 171 180 139 1
40 137 Temperature, lower quenching water speed, 4.0 4.0 18.0
7.0 7.0 7.0 7.0
7.0 7.0 7. OGPM scrubber's 130 137 120 1
25 130 130 130.5 118
116 108 Inflow temperature, lower inflow pressure, H20 -1.8 -1.4 -1.9
-2.0 -2.0 -2.0 -1.6
-1.5 -1.5 -1.4 Scrubbing
53 52 72 75 76
75 36 36 34 32 Mixture speed, GPM scrubbing 69 64 82
84 85 88 48 48
48 50 Mixture rate, GPM/1 o o o ACF Separator effluent gas 127 127 104 1
06 129 128 130.5 119
118 111 Temperature, to lower scrubber 127 126 100
105 129 128 130.5 129
Temperature of scrubbing mixture of 106 106 to lower separator drum - 107 111
130.5 130 130.5 119
Temperature of scrubbing mixture of 118 109, to lower scrubber 5.5 5.7 6.0
6.8 6.7 6.7 6.5
pH of scrubbing mixture of 6.9 7.4 8.0 Scrappano 0.59 0.59 0.8
0.8 0.8 0.8 0.49
0.49 0.49 0.49 Nozzle orifice size, in Nozzle pressure, 110 110 100
100 100 100 125
125 100 100 psig Experiment HI JKLMNOPQ Influent Sample: Amount of catalyst, g. 0448. 0693. 0674.
0597. 0624. 0427. 0379. 0
512.0422. 0377 Ren/SCF Inorganic condensate, . 0196. 0135. 0156
．． 0173. 0181. 0133. 0094.
0151. Q136. 0156 Gray/S C F Organic Condensables, . 0189. 0054. 0053
．． 0074. 0063. 0059. 0119.
0085. 0051. 0038 grain: /SCF whole grain, g. 0833. 0882. 0383.
0844. 0368. 0619. 0592. 0
748. 0609. 0571 Ren/SCF so2 content, 465 630 588 -
554 560 607 540 360
341 wppm effluent sample: amount of catalyst, g. 0039. 0035. 0018.
0024. 0044. 0028. 0021. 0
037. 0020. 0043 Ren/SCF Inorganic Condensate Warfare. 0080. 0054. 0034.
0024. 0059. 0035. 0041. 0
040. 0032. 0028 Grain CF Organic Condensables,. 0060. 0022. 0029
．． 0020. 0023. 0035. 0070.
0055. 0015. 0035 Gray 7/S CF Whole grain, G. 0179. 0111. 0081.
0063. 0126. 0093. 0132. 0
132. 0067. 0106 Ren/SCF SO2 content, None 4.4 2.2 None
None 4.3 4.3 None None None wppm As can be seen from the data in Table 2, experiments H and Ta.

Although the data from these short-term experiments appear to indicate that the method can be practiced over a wide range of pH values, maintaining the pH between 6 and 7 is preferred for operability in continuous operations such as industrial-scale processes. It turned out to be necessary.

At higher pH values, C02 absorption in the aqueous scrubbing mixture results in increased caustic consumption as well as undesirable carbonate formation.

Low pH operation is undesirable as it results in increased corrosion rates of the equipment.

[Brief explanation of the drawing]

The accompanying drawings are a schematic flowchart of one embodiment of the invention, the main parts of which are indicated by the following reference numerals. 1: Catalyst regenerator, 2: CO boiler, 3: Venturi scrubber, 4: Separator drum, 5: Gas heater.

Claims (1)

Claims: 1. Sulfur dioxide and cracking catalyst fines from a gaseous effluent containing sulfur dioxide and cracking catalyst fines, the catalyst fines comprising up to about 40% by weight of particles less than 1 micron in size. Upon removal, (a) introducing said gaseous effluent into a Venturi structure and dispensing with said gaseous effluent containing a basic material selected from the group consisting of alkali metal hydroxides, ammonium hydroxide, and ammonia; 6 to about 7
(b) increasing the velocity of said mixture of gas and scrubber mixture through a constricted passageway of said penturi structure; (C) recovering the mixture from step (b) from the venturi structure; and (d) separating said recovered mixture into a gaseous portion and a liquid portion having reduced catalyst fines and sulfur dioxide content. A method for removing sulfur dioxide and cracking catalyst fines from a gaseous effluent comprising: 2. The method of claim 1, wherein 1 to 40% by weight of the catalyst fines is less than 1 micron in size. 3. The method according to claim 1, wherein the basic substance is sodium hydroxide. 4. A method according to claim 1, comprising recycling a portion of the separated liquid portion to the gas-scrubbing mixture contacting step (a). 5. Claim 1 comprising contacting the gaseous effluent with water prior to introduction of the venturi structure of step (a).
The method described in section. 6. A method according to claim 1, comprising introducing the gaseous effluent into the venturi structure of step ia) without a water pretreatment step. 7. A method according to claim 1, comprising preheating the gaseous portion obtained in step (d) above its dew point. 8. The method of claim 1, wherein the gaseous effluent is a gaseous mixture produced in a regeneration zone of a catalytic cracking process. 9. The method of claim 1, wherein the gaseous effluent is a gaseous mixture produced by burning the effluent of a regeneration zone of a catalytic cracking process in a combustion zone. 10 The high velocity flow of the aqueous scrubbing mixture is approximately 5 to
The method of claim 1 comprising cooling by about 50 degrees Fahrenheit. 11. The method according to claim 1, wherein the catalyst fine powder contains a siliceous material. 12. The method of claim 1, wherein the catalyst fine powder comprises amorphous or crystalline silica alumina or a mixture thereof.