JPS6034413B2 - Method for regenerating carbonaceous adsorbent used for flue gas treatment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regenerating a carbonaceous adsorbent that has been exhausted by contact with exhaust gas containing sulfur oxides, and more specifically relates to a method for regenerating a carbonaceous adsorbent that has been exhausted by contact with a sulfur oxide-containing exhaust gas. The present invention relates to a method for recovering concentrated sulfur dioxide gas in a state substantially free of sulfur trioxide and ammonia, and regenerating exhausted adsorbents to a state where they can be reused for exhaust gas treatment.

A flue gas treatment method in which ammonia is injected and mixed into flue gas containing sulfur oxides and brought into contact with a carbonaceous adsorbent such as activated carbon not only effectively removes sulfur oxides from flue gases, but also When nitrogen oxides coexist therein, it has the advantage that these nitrogen oxides can also be removed at the same time.

In this case, sulfur oxides in the exhaust gas are adsorbed on the carbonaceous adsorbent as sulfuric acid, acidic ammonium sulfate, ammonium sulfate, etc., while nitrogen oxides are decomposed into nitrogen and water by the action of ammonia as a reducing agent. Therefore, the carbonaceous adsorbent used in this flue gas treatment method gradually becomes exhausted as sulfuric acid or sulfate accumulates on the surface of the adsorbent over time of contact with the flue gas. If this is heated and regenerated at an appropriate time, it can be reused for the above-mentioned flue gas treatment. During this heating and regeneration, sulfur dioxide gas with a relatively high concentration is obtained, and sulfuric acid or sulfur can be recovered from this gas. However, the relatively high concentration of sulfur dioxide gas produced as a by-product in the conventional thermal regeneration method is not without problems in that it also accompanies sulfur trioxide and ammonia. That is, in the conventional heating regeneration method, the exhausted adsorbent is usually heated to 300 to 650
A method of contacting with an inert gas at an elevated temperature of o0,
Through this contact, sulfuric acid, sulfate, and ammonia on the exhausted adsorbent are decomposed as shown in the following equation, and the exhausted adsorbent is regenerated.

24S040C → 020C0212L
Ozu & HS04 → NH30$020N20mother L03 (NH,)2S04→ 4NH30$020N20mother L02/Karihi 30(0)*1 1
Nosu 20 ratio 0 *means nitric oxide on the surface of the adsorbent.These decomposition products are purged from the adsorbent by an inert gas, so a relatively high concentration (approximately 25-30%) of sulfur dioxide is produced. As is clear from the decomposition reaction equation above, this byproduct gas not only contains ammonia but also contains 0.0% sulfur trioxide, which is not reduced to sulfur dioxide, per volume of sulfur dioxide. About 0.001 to 0.01 volume is accompanied.

Therefore, when attempting to recover sulfuric acid or sulfur from this type of by-product gas, one must be prepared for clogging of the recovery equipment and reduction in product purity due to ammonia and sulfur trioxide. The present invention enables the recovery of relatively high-concentration sulfur dioxide gas, which is produced as a by-product during the regeneration of exhausted adsorbents, in a state substantially free of sulfur trioxide and ammonia, and allows the exhausted adsorbents to be reused for exhaust gas treatment. Provide a way to play to the state. A method for removing sulfur trioxide from the relatively high concentration sulfur dioxide gas produced by-product during regeneration while regenerating the exhausted adsorbent by heating is disclosed in Japanese Patent Application Laid-Open No. 52-10.
This method is clearly distinguished from the present invention in that sand or the like is used as a heating medium for the exhausted adsorbent and that ammonia is not included in the by-product gas during regeneration. Ru.

Also, JP-A-52-71373 and JP-A-52-688
Publication No. 58 describes a method of catalytically decomposing ammonia in exhaust gas with coexisting oxygen (small H303Q→20 fine 20). The present invention also differs from the ammonia decomposition method described above in that the relatively high concentration iogas contains almost no oxygen. Therefore, the method for regenerating an exhausted carbon cost adsorbent according to the present invention is as follows: [a] The exhausted adsorbent is caused to flow down as two upper and lower moving beds, and [b] The upper moving bed has a first gas flow as described below. and the fatigue adsorbent, about 150 to 35,000
to cause the sulfur trioxide and ammonia in the first gas stream to be captured by the exhausted adsorbent, and to form a second gas stream substantially free of sulfur trioxide and ammonia and containing a relatively high concentration of sulfur dioxide. A gas stream is withdrawn from the moving bed and the exhausted adsorbent, which has captured sulfur trioxide and ammonia, is transferred to the lower moving bed where the exhausted adsorbent is heated at about 300-650°C. The exhausted adsorbent is regenerated by contacting it with an inert gas at an elevated temperature of The gas stream taken from the top of the lower moving bed is fed as the first gas stream to the upper moving bed, and the regenerated adsorbent is transferred to the lower moving bed. It is characterized by being collected from the bottom.

That is, in the present invention, if the first gas stream by-produced during the regeneration of the exhausted carbonaceous adsorbent is brought into contact with the exhausted carbonaceous adsorbent during the regeneration at a temperature of about 150 to 35 pi The property that sulfur trioxide and ammonia mixed with sulfur dioxide are captured by the exhausted carbonaceous adsorbent according to the following equation is utilized.

S03 Toka 20 → Sun 2S04 NH3 Toka 2S04 → NH4HS04 NH3 Ten NH4HS04 → (NH4)2S04 In this case, the amount of sulfuric acid required to collect the ammonia in the first gas flow is the sum of the first gas flow and exhaustion adsorption. Although it depends on the contact temperature with the agent, generally 0.5 to 1 mol per mol of ammonia.
Preferably 1 to 2 moles of sulfuric acid are required.

However, this amount of sulfuric acid can be easily maintained by adjusting the amount of exhausted adsorbent flowing down as a moving bed. The present invention will now be described in more detail with reference to the accompanying drawings.

The carbonaceous adsorbent exhausted by contact with the sulfur oxide-containing exhaust gas injected with ammonia is fed into the regenerator through the top valve V of the regenerator 1. In the regenerator, the exhausted adsorbent flows down as moving beds in two stages, upper and lower. Contact at ~300k0. This contact traps the sulfur trioxide and ammonia in the first gas stream in the form of sulfuric acid or sulfate on the exhausted adsorbent. The exhausted adsorbent that has captured sulfur trioxide and ammonia moves from the upper moving bed 2 to the lower moving bed,
It flows down through the plurality of heat transfer tubes 4 while coming into contact with the inert gas supplied from the line 3. The heat exchanger tubes 4 are arranged approximately vertically in a heating region 5, which heating region is supplied with heating gas flowing in a line 6. The inert gas and exhausted adsorbent flowing down in the heat exchanger tube are heated to a regeneration temperature of about 300 to 650 degrees by indirect heat exchange with the heated gas, whereby the exhausted adsorbent becomes sulfur dioxide, sulfur trioxide, and In addition to being regenerated by releasing ammonia, etc., sulfur dioxide,
Sulfur trioxide, ammonia, etc. are purged from the regenerated adsorbent by an inert gas. Next, the regenerated adsorbent descends to the separation region 7 together with the inert gas, and in this region, the inert gas accompanied by sulfur dioxide, sulfur trioxide, and ammonia is separated from the regenerated adsorbent. It is taken out of the regenerator through a valve V2 provided at the bottom of the regenerator, and is reused for contact with exhaust gas. On the other hand, the gas stream separated from the regenerated adsorbent is sent from the top of the separation zone 7 via line 8 to the upper moving bed 2, where the sulfur trioxide and ammonia in the gas stream are transferred to the exhausted adsorbent. Since the sulfur dioxide gas is trapped, a relatively high concentration of sulfur dioxide gas, which is substantially free of sulfur trioxide and ammonia, can be taken out from the upper part of the moving bed 2 into the line 10. In addition, the code|symbol 9 in a figure shows a rectifier. As is clear from the above, according to the method of the present invention, not only can the carbonaceous adsorbent exhausted by contact with exhaust gas be regenerated into a reusable state, but also the carbonaceous adsorbent that is Relatively high concentrations of sulfur dioxide can be recovered in a state that does not contain sulfur trioxide or ammonia, so even if the byproduct gas is supplied to sulfuric acid recovery or sulfur recovery equipment, there is no need to worry about garden debris clogging the equipment. There is no need to worry about deterioration of product purity.

Example 1 Activated carbon that adsorbed 165 sulfuric acid per g of activated carbon was
02 willow, packed in a counter-current moving bed adsorber with an effective filling height of 1000 ribs, S0215%, Chord 030%, C029%, S
Highly concentrated S02 gas containing 030.08%, NH30.2%, and N2 45.72% was supplied at a reaction temperature of 270 oo and a flow rate of 1 hour.

At this time, the residence time of the catalyst in the adsorber was set to 3 hours. When NH3 and S03 in the adsorber outlet gas were analyzed, the concentration of NH3 was 0.0003% and S03 was not detected. Note that each gas concentration is expressed on a wet basis. Example 2 Activated carbon used for desulfurization and denitrification of boiler exhaust gas (SO reed - 9/g activated carbon with an adsorption amount of 107, N ratio + 9/g activated carbon with an adsorption amount of 11.8) was added to the regenerator shown in the drawing. 223k
It was supplied and regenerated at 9/hour.

The residence time of the activated carbon in the heat transfer tube was 1 period, and the temperature of the regenerated activated carbon finally obtained was 400°C. Also,
The amount of inert gas supplied from line 3 was 3/hour. At this time, the composition of the desorption gas obtained in line 8 is S〇210-0%, C〇28-8%, C〇〇. 5%, 2032-3%, S030.05%, NH30.30%, N
It was 248.05%, and the gas amount was 5 s/hour.
This gas is transferred to the upper moving bed 2 of the regenerator (activated carbon filling volume 0
．． 232). As a result, NH3 in the gas leaking out from line 10' was 0.0002%, and S03 was not detected. Note that each gas concentration is expressed on a wet basis.

[Brief explanation of the drawing]

The drawing is a longitudinal cross-sectional view of a regenerator through which the invention is implemented.

Claims (1)

[Claims] 1. In a method for regenerating a carbonaceous adsorbent that has been exhausted by contact with a sulfur oxide-containing exhaust gas injected with ammonia, (a) the exhausted adsorbent is caused to flow down as a two-stage moving bed, ( b) in the upper moving bed, a first gas stream described below and an exhausted adsorbent are brought into contact at a temperature of about 150 to 350°C, and sulfur trioxide and ammonia in the first gas stream are captured by the exhausted adsorbent; A second gas stream substantially free of sulfur trioxide and ammonia and containing a relatively high concentration of sulfur dioxide is withdrawn from the moving bed, and the exhausted adsorbent having captured sulfur trioxide and ammonia is transferred to the lower stage. (c) In the lower moving bed, about 30% of the exhausted adsorbent was
The exhausted adsorbent is regenerated by bringing it into contact with an inert gas at an elevated temperature of 00 to 650°C, and sulfur dioxide, sulfur trioxide, ammonia, etc. released during this regeneration are purged from the adsorbent with the inert gas. and (d) supplying the gas stream taken out from the top of the lower moving bed as the first gas stream to the upper moving bed to remove the regenerated adsorbent. A method for regenerating exhausted carbonaceous adsorbent, which comprises recovering the carbonaceous adsorbent from the bottom of a lower moving bed.