JPH02699A - Removal of carbon dioxide and moisture from gas in town gas production process - Google Patents

Abstract

PURPOSE:To decrease separation loss by removing CO2 and moisture from a produced gas by the pressure-swing process, recycling part of the desorbed gas to the produced gas and using part of the purified gas as a rinsing gas. CONSTITUTION:A produced gas from a town gas production process is passed through four adsorption towers A-D and is purified by adsorbing CO2 and moisture. The desorbed gas is passed through a cooling tower 15 and a surge tank 16 to a calorific value control apparatus. Part of the desorbed gas is passed through a water-containing gas holder 12, pressurized with a compressor 14, and led through a cooler 17 and a water separator 18 to an adsorption tower 18, where it is readsorbed and recycled to the produced gas. On the other hand, part of the purified gas is passed through a flow control valve 20 and used as a pressurizing gas for increasing the pressure in the adsorption tower in which adsorption is performed in the next cycle or as a rinsing gas for replacement of pipes.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is used to purify generated gas in the city gas production process, particularly to remove carbon dioxide, which is a non-combustible component, from the generated gas, and moisture that is harmful to corrosion of pipes, etc. Regarding how to remove.

(Background of the Invention and Prior Art) When producing high-calorie city gas such as alternative natural gas (SNG), a gas generator is generally used as a production method to produce H2, C1 (4, CO, CO2°N2, Generate a mixed gas such as H20, and remove CO2 and H2 in this mixed gas.
0 is separated and removed, and the heat is increased to adjust the heat hi and combustibility to a predetermined value.

This separation and removal of CO2 and H20 has conventionally been carried out using two processes: a wet decarboxylation device that absorbs and removes the gas in an absorption liquid such as potassium carbonate, and a dehydration device that cools the gas and separates condensed water. In this case, not only complicated operations are required to start up and change the load, but also a long time is required until the process stabilizes, resulting in poor operability and economic efficiency, and a solution to this problem has been desired.

CO2, H20: 1 If only made of F5, 1 Brefushi
If the double-swing method is used, separate devices for decarboxylation and dehydration are combined into one, and the device and operation become simpler. However, when incorporating it into the city gas production process using conventional methods,
There is a gas generator in the upstream and a heat adjustment device in the downstream, which must be compatible with continuous flow, and the difficulty of the pressure swing method is that fluctuations in flow (h), pressure, and heat soaking cannot follow the process. In addition, exhaust gas (res.1-gas) containing a large amount of combustible components is generated, which is not only difficult to dispose of, but also causes the loss of the effective components of city gas, making it difficult to use in practical equipment. was not adopted as

(Problems to be Solved by the Invention) The problems to be solved by the present invention are to recover as much as possible of city gas active components (combustible gas) in the exhaust gas (rest gas) generated by the pressure swing method, minute I11
Reduces losses and reduces fluctuations in flow rate, pressure, and heat h1 by 1
14 This is to ensure that it does not affect the subsequent process.

(Means for Solving the Problems) The technical means taken by the present invention to solve the above problems is to remove carbon dioxide and moisture from the generated gas in the city gas production process using four or more adsorption towers. The desorbed gas is adsorbed and purified using a pressure swing method that uses cycles, and a part of the desorbed gas is brought to a constant pressure and constant calorific value in a water-filled gas holder equipped with a homogenizer, and then re-adsorbed through the adsorption tower used for adsorption in the moe process. While recycling the purified gas into generated gas, a part of the purified gas is used as boosting gas for pressurization of the adsorption tower and tin gas for replacing piping etc. through a constant flow control valve to continuously purify gas. It is something to do.

As the adsorbent, a carbon molecular sieve having an average pore diameter of about 3 pores is used.

In the depressurization step of the pressure swing method, the pressure is reduced from both the top and bottom of the adsorption tower at the desired amount, and the reduced pressure gas is supplied as a primary process gas from both the top and bottom of the adsorption tower in the pressurization process cycle.

In addition, the desorption gas to be recycled is adsorbed in the pressurization process cycle. Except for what is supplied to S as the primary pressurized gas, the depressurization gas is up to 500 rorr.

Furthermore, the recycle gas is supplied to the adsorption tower at a cool temperature up to the adsorption temperature until the final stage of the recycling process, and is adjusted to the desorption temperature at the final stage of the culm.

In this invention, the generated gas refers to the raw material Naf No., LP
G, C where methanol is reacted with water vapor and 1 is removed.
A wet gas mixture whose main combustible components are H4 and H2 and which also contains CO2.

(Summary of the Invention) In the following explanation, the gas generated in the city gas production press (hereinafter referred to as the gas generated from the processing cylinder) is CH4, which is generated in the production process of producing city gas using methanol as a raw material, for example. To-1z is the main combustible component,
It is a mixed wet gas containing CO2, which is continuously sent at a constant pressure and fixed amount from a gas generator.

The pressure of the gas generated in the processing cylinder is determined by the reaction pressure of the gas generator, and will be explained as 9 kg/G in the following explanation.

The gas generated from the processing cylinder is introduced into an adsorption tower of a pressure swing apparatus (hereinafter referred to as PSA apparatus), and CO2 and H2O are adsorbed onto an adsorbent filled in the adsorption tower, and the gas is taken out as purified gas after treatment.

A carbon molecular sieve with an average pore size of about 300 ml is used as the adsorbent.

By using the adsorbent, the method of the present invention does not require a pretreatment step for moisture removal, and there is no need to install a moisture removal treatment device, making it possible to downsize the device and reduce costs. Become.

In the present invention, the PSΔ device has four adsorption towers (A
, B, C, D> and a suction pump, right water type gas holder, and compressor, it is a 4-column type that repeats 10 steps of 4 cycles of adsorption, re-adsorption, depressurization, and pressurization. As shown in the process block diagram in the figure, when the A tower is in the adsorption process, the B tower is in the re-adsorption process, the D tower is in the pressure equalization/autostatic pressure reduction/suction pressure reduction/suction release process, and the D tower is in the primary pressurization ( Equal pressure)・
A secondary pressurization step is performed, and the gas flow shown in Table 1 is operated in five steps.

That is, a part of the treated purified gas taken out from /15 is continuously used as the secondary pressurized gas of the D tower and the rinsing gas of the recycle circuit so that the pressure and flow rate do not fluctuate.

At the beginning of the pressure equalization process of C'7), there is a highly pure combustible component in the upper part of the column, which is the result of CO2 removed from the recycled gas by re-adsorption in the previous recycling process. By connecting the lower and lower parts, the pressure in the D column is reduced from the upper and lower parts of the column, and the reduced pressure gas is allowed to flow Δmm into the upper and lower parts of the column as the primary pressurized gas of the D column.

In the above-mentioned movement of gas from both directions, the highly pure combustible components in the upper part of the tower and the combustible components of the pre-processed recycled gas in the lower part of the tower are both discharged from the D tower to the D tower and are not left behind. It has the effect of increasing purity. In addition, highly pure combustible components are fed into the upper part of the D column and unprocessed I-cycle gas is fed into the lower part of the D column.
This results in a gas component distribution close to that of the adsorption regime, which has the effect of increasing the component purity of the purified gas after treatment.

Therefore, the purified gas purity and the exhaust gas purity are increased.

Next, the self-pressure reduced gas of the D tower is sent to a water-type gas holder with 8 equalization positions, and when the pressure of the D tower is almost equal to that of the water-type gas holder, it is switched to the desorption gas suction pump and the pressure is increased to 500T.
The gas is sucked up to about 100 ml of water and sent to the same water-type gas holder.

As mentioned above, the self-pressure reduced pressure gas and the suction reduced pressure gas that still contain combustible components, that is, the recycled gas, are stored in a water-filled gas holder equipped with an equalization device because the heat of the desorption gas fluctuates depending on the timing of supply. This has the effect of making m substantially uniform and also making constant the suction pressure and discharge pressure of the recycle gas compressor, which will be described next.

The recycled gas, which has almost uniform pressure and calorific value, is processed by the recycled gas compressor to absorb B, which has remaining adsorption capacity.
The remaining carbon dioxide gas is adsorbed again through the column, separated, and returned to the gas generated from the treated surface.

In addition, using this recycling circuit, the treated gas at the end of the recycling process is transferred to a water-type gas holder and a recycling AI.
: Incorporating a feed-replacement 161 rinsing process into the pipe, and increasing the moisture content of the combustible gas in the purified gas in the [Next] Noicle. This method has the effect of minimizing the amount of combustible components in the exhaust gas by recovering combustible components without affecting the upstream stream of the PSA device, and minimizing the calorific value fluctuation and pressure fluctuation of the downstream purified gas.

(Detailed Description of the Invention) The present invention will be described in more detail below based on the flow sheets shown in FIGS. 1 and 2.

The method of the invention is carried out by the apparatus shown in FIG.

That is, the four adsorption towers A, B, C, and D, the water-based gas holder 12, the IIQ gas suction pump 13, the recycle gas combiner 14, and several other necessary devices communicate with each other via piping. Valve 1A~ID, 2A~2D, 3A~30°4A
~4D, 5^~5D, 6^~6D, 7. 8. 9
．． 10. By opening and closing 11, the gas flow is switched and controlled, and the 5 steps described above
Cycle 10 steps are repeated continuously.

The operation development of the adsorption towers A, B, C, and D is shown in Table 2, and for this purpose, the valves are opened and closed as shown in Table 3.

(Person 3) Open and close the buttons of each step between X rl and close Next, the content of steps during the purification process of the adsorption tower and the Δ tower will be explained with reference to FIGS. 2 and 4.

When the Δ tower is in the purification process, the J and B towers (not shown in Figures 2 and 4) are in the re-adsorption (recycling) process, and the C tower is in the depressurization process, which consists of equalization, autogenous pressure reduction, suction depressurization, and suction discharge processes. Process, DJh
uses a pressurization process consisting of a primary pressurization (pressure equalization) and a secondary pressurization process.

In step 1, valves 1A, 28, 3B, 4A, 5C
, 50, 6C96D is closed, and the treated generated gas (■) introduced into the A column causes the adsorbent to adsorb CO2 and Hz O.
Purified gas ■ becomes purified gas cooler 15. The purified gas flows through the purified gas surge tank 16 to a heating step by adding butane to the city gas production process. The Nycle gas stored in the water-type gas holder 12 is transferred to the recycled gas cooler 17 by the recycled gas compressor 14.
The recycled gas is introduced into the B tower via the water separator 18 and continues to be recycled into re-adsorbed and treatable generated gas (2).

The above adsorption and recycling are continuously performed from step 1 to step 5.

Since the temperature of this recycled gas (■) increases due to promotion, it is cooled down to the adsorption temperature in the recycled gas cooler 11, but at the end of the recycling process, the recycled gas cooler 11 is bypassed in preparation for desorption in the next cycle of tower B. Or reduce the amount of cooling water to adjust to the desorption temperature. Therefore, since the adsorption temperature can be lowered and the desorption temperature raised higher, the conditions for adsorption and desorption become very advantageous.

On the other hand, the C tower performs desorption, but because it was used for recycling in the previous process, it has a pressure of 9 ka/cdG.
In step 1, primary pressurized gas (2) is fed from both directions from the upper and lower parts of the C tower to the upper and lower parts of the D tower, which was used for desorption in the previous recycle and has no remaining pressure, to equalize the pressure in the D and C towers. As a result, the pressure in tower C and tower D is approximately 4.5kc.
It becomes l/a+fG.

Highly pure combustible components are transferred to the primary pressurized gas sent to the upper part of the D tower.

In addition, a part of the purified gas (■) after treatment is used as a secondary pressurized gas (■) to increase the pressure of the D tower in preparation for the next cycle of adsorption.
It is supplied to the D tower as

At this time, a constant flow control valve 20 is installed in the outlet piping from purified gas (2) so that the pressure and flow 61 do not fluctuate.
Supply at a constant flow rate so that the pressure does not fluctuate.

Next, in step 2, by closing valve 6D and listening to valve 8 instead, the C tower is depressurized to the holder pressure of the right water type gas holder 12 (approximately 200 m1H20) - its self-pressure reduced gas is sent to the right-hand type gas holder 12 via the desorption gas cooler 19.

In step 3, valve 8 is closed, valves 9 and 10 are turned on, and desorption gas suction pump 13 is operated to suction and depressurize the C tower to approximately 500 Torr, and the suction depressurized gas ■
is sent to the right water type gas holder 12.

Further, in step 4, the valve 10 is closed and the valve 11 is replaced.
By listening to this and reducing the pressure to 50 Torr with the desorption gas suction pump 13, the
The CO2 and H20 desorbed up to r are discharged as exhaust gas (■). In this regeneration of the adsorbent by the desorption gas suction pump 13, the exhaust gas density decreases as the degree of vacuum increases due to the exhaust characteristics of the pump 13. In addition, as the degree of vacuum increases, CO2 increases as a component in the reduced pressure gas, and CH4/C0
, 2 becomes smaller.

Furthermore, in step 5, the valve 5D is closed, the valve 7 is opened instead, and a portion of the purified gas ■ taken in via the constant flow control valve 20 is sent to the aqueous gas holder and recycling piping as 0 gas. Enter.

Replacing this recycle circuit with purified gas has the effect of increasing the combustible gas concentration of the purified gas after treatment in the next cycle. Further, in step 5, the D tower is left in an idle state.

Figure 3 shows the pressure change inside the adsorption tower at each step. As can be seen from this, when the adsorption tower connected to the main line of Cores, that is, the adsorption tower that is performing adsorption, changes the cycle, the pressure of the adsorption towers before and after is almost the same (
9kg/c++fG), so there is no pressure shock when switching.

Also, the composition of each part of the gas in this series of steps.

Table 4 shows the results of examining the flow rate and calorific value using practical examples.

(Table 4) f'lIX Gas % % k caf/N As is obvious from the above Table 4, according to the method of the present invention, 1! - By the swing method, an extremely high percentage of the city gas active components in the exhaust gas are recovered, and the exhaust gas contains almost no combustible components. In addition, the re-adsorption process is carried out on the S1 Noicle gas in a dedicated adsorption tower, but since the recycled gas has a high partial pressure of CO2 and a low partial pressure of CH4, the adsorbent has an increased adsorption capacity for CO2 and a CH4 Adsorption capacity decreases. This phenomenon is effective because three carbon molecular sieves are used as adsorbents.

Therefore, re-adsorption is possible and the amount of recycled gas is extremely small.

(effect) Since the present invention has the above configuration, it has the following advantages.

(1) Since the desorbed gas is recycled and re-adsorbed during the recycled gas process, the effective components of city gas in the exhaust gas generated by the pressure swing method can be efficiently recovered, and separation loss is extremely small. can do.

Therefore, not only does the calorie increase rate of the purified gas become high, but also the exhaust gas contains very few combustible components and there is no problem even if it is released into the atmosphere as it is, so the cost for exhaust gas treatment is also reduced.

Since the neucle gas is re-adsorbed through a dedicated adsorption tower, the amount of recycling can be reduced for the reasons mentioned above, and the capacity and cost of this equipment can also be reduced.

(2 Recycled gas is temporarily stored in a water-filled gas holder,
After passing through the adsorption tower! 2! The gas generated before X-processing is recycled, and a portion of the gas is taken out from the purified gas for pressurization and rinsing through a constant flow control valve so that the pressure of the purified gas does not fluctuate, so the conventional pressure swing method is not continuous. Fluctuations in pressure, flow rate, and heat amount, which are problems in processing, can be eliminated, and the influence on the upstream and downstream of the PSA device, that is, the gas generator and the heat adjustment device, can be almost eliminated. There is no fear of heat h1 fluctuations in the product gas.

(3) In the pressure equalization step, the upper and lower parts of the adsorption tower on the depressurizing side and the pressurizing side are connected, and gas is moved from both directions. This allows the adsorption tower on the vacuum side to
1! Since both the highly combustible components and the combustible components of the unprocessed recycled gas at the lower part of the column are discharged to the pressure-side adsorption column and do not remain, the purity of the desorbed components during desorption is increased. In addition, in the pressure-side adsorption tower, highly pure combustible components are fed into the upper part of the tower and unprocessed recycled gas components are fed into the lower part of the tower, resulting in a gas component distribution similar to that of the purification (adsorption) system in the next cycle. The component purity of the purified gas after treatment is increased. Therefore, the purity of purified gas and the purity of exhaust gas can be increased.

(4) Excluding what is supplied as the primary pressurized gas to the adsorption tower in the pressurization process cycle, the reduced pressure gas up to 500 Torr, that is, the recycled gas, is CO from the gas generated in the processing section.
An adsorbent that processes this gas, which has a high partial pressure of CH2 and a low partial pressure of CH4, has an improved C○2 adsorption capacity and a decreased Cth adsorption capacity, compared to when it processes the gas generated from the processing section. Therefore,
It is possible to re-adsorb CO2 with the adsorbent that adsorbed it in the previous cycle, allowing more CO2 to be adsorbed to the adsorbent and making CO2 desorption advantageous.

(5) Since the temperature of the recycled gas rises due to pressure increase, it is cooled down to the adsorption temperature. However, at the end of the process, the temperature is adjusted to the underwear temperature, so the adsorption temperature can be lowered and the desorption temperature raised higher. And the conditions for attachment and detachment become very advantageous.

(6) Since a carbon molecular sieve with an average pore diameter of approximately 3 mm was used as the adsorbent, no pretreatment for removing moisture was required. Therefore, the device becomes smaller and the equipment cost is reduced.

[Brief explanation of the drawing]

Figure 1 is a flow sheet showing the schematic configuration of an apparatus for carrying out the method for removing carbon dioxide and moisture from gas in the city gas production process of the present invention, and Figure 2 explains the principle of the method of the present invention. Flow sheet, Figure 3 is a graph showing each step of the method of the present invention and the pressure change inside the adsorption tower at each step, Figure 4 is a process block diagram, and the figure in parentheses shows the case of the A column viscous production (adsorption) process. It is something.

Claims (1)

[Claims] 1) Carbon dioxide and moisture in the gas generated in the city gas production process are adsorbed and purified by a pressure swing method that uses four or more adsorption towers in cycles, and a part of the desorbed gas is purified. After equalizing the pressure and heat in a water-containing gas holder, it is re-adsorbed through an adsorption tower and recycled into generated gas, while a portion of the purified gas is passed through a constant flow control valve to perform the adsorption process in the next cycle. A method for removing carbon dioxide and moisture from gas in a city gas production process, characterized by continuously purifying the gas by using it as a pressurized gas for pressurization and a rinsing gas for replacing pipes, etc. 2) The method according to claim 1), wherein a carbon molecular sieve having an average pore diameter of about 3 Å is used as the adsorbent. 3) The depressurization process in the pressure swing method is characterized in that the pressure is reduced from both the top and bottom of the adsorption tower at the initial stage, and the depressurized gas is supplied from both the top and bottom as the primary pressurized gas to the adsorption tower in the pressurization process cycle. The method according to claim 1). 4) The desorption gas to be recycled excludes that supplied as the primary pressurized gas to the adsorption tower in the pressurization process cycle.5
The method according to claim 1), characterized in that the gas is a reduced pressure gas of up to 000 Torr. 5) The method according to claim 1, wherein the desorption gas to be recycled is cooled to the adsorption temperature until the end of the recycling process, and adjusted to the desorption temperature at the end of the process. 6) The pre-treatment gas is a generated gas obtained by reacting the raw materials naphtha, LPG, and methanol with steam, and contains CH_4,
The method according to claim 1), characterized in that the mixed wet gas contains H_2 as a combustible main component and CO_2.