JPS6283020A - Method of controlling switching regenerated adsorption tower - Google Patents

Abstract

PURPOSE:To prevent fluidization and powdering of adsorbents, by making the direction of a gas flow in a packed layer in running downward at both of absorption and desorption operations and switching a valve at the time of adsorption and desorption to open and close an outlet and inlet valves simultaneously. CONSTITUTION:An adsorption tower A is adsorbing and an adsorption tower B is under regeneration. In order to switch the adsorption tower A to a regeneration mode and the adsorption tower B to an adsorption mode, V11 and V14, V12 and V13, V21 and V24, and V22 and V23 are simultaneously opened or closed at respective inlet and outlet, and a reduction ratio of a motor is adjusted such that a closing speed is for one min., and an opening speed is for two min., thereby effecting stable switching operations. Both adsorption and desorption are operated in such a manner that the gas flows downwardly, thereby preventing fluidization and powdering of the adsorbent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an adsorption tower control method in which two or more adsorption towers filled with adsorbent are operated by switching valves.

[Conventional technology]

In plants that involve cryogenic separation processes such as LNG and LPG recovery equipment, in order to avoid equipment troubles due to freezing,
It is necessary to remove moisture to below 14%. Moisture is also removed as a pretreatment in other chemical plants where moisture has an adverse effect on the performance of catalysts and adsorbents (for example, in the Co5orb method and the CO absorption separation method using CuC/2/AlCl3).

In such cases, two or more dehumidification towers filled with a moisture absorbent such as Molecular Sheep are installed, and these are switched alternately so that the absorbent that has absorbed moisture follows the high-temperature gas at 200 to 300°C. It is common to regenerate and use repeatedly.

Generally, a 4A-type extruded cylindrical adsorbent with a diameter of 3 to 5% and a length of 5 to 7% is used for dehumidification molecular cylinders in LNG plants, and adsorbs at room temperature to about 50°C. (6~
12 hours), then switch the two towers by valve operation, and heat a part of the process gas after water adsorption in a heating furnace at 250-300°C.
A cycle operation is set up in which the adsorbed moisture is expelled by passing gas heated to 100°C, regenerated, cooled, and then switched using a valve to perform the adsorption operation again.

The second example shows an example of a natural gas purification process and a conventional valve-switchable packed column adsorption/dehumidification system incorporated therein.
As shown in the figure. In Figure 2, the natural gas is
After removing 2S and entrained mist in the flash drum 2, the moisture in the gas is passed through an adsorption tower 3 filled with a moisture absorbent such as molecular sheep to avoid freezing problems in the downstream cryogenic separator. It is dehumidified until the concentration is below a few degrees. The adsorption operation is carried out at a temperature of 20 to 30 atm and room temperature to 35°C. The adsorption tower is A-B... 2 or more towers are incorporated and 4 to 1
It is alternately switched by operating a valve every two hours, and adsorption regeneration is performed alternately and used repeatedly.

In the regeneration operation, a part of the purified gas is extracted from the middle stage of the compressor 4 in the latter stage and heated to 250 to 300°C in the heating furnace 5.
The adsorbent is regenerated by passing it through an adsorption tower 3 that has adsorbed water, and then it is cooled with cold gas and used repeatedly. These heated gases and cold gases are cooled by a cooler 6, drained by a flash drum 7, and then returned to the front of the desulfurization tower 1 as a process gas. In this way, when a part of the process gas is heated and used as regeneration gas and returned to the process, the regeneration operation requires 1 to 3 times higher pressure than the adsorption operation (
Become.

In addition, the regeneration gas is often used as general heating fuel gas inside and outside the process without returning it to the process, and in this case the operating pressure ranges from several Kp/cn1G to several tens of Kf/c.
rA a, the operating pressure is significantly different between adsorption operation and regeneration operation, and sudden pressure fluctuations occur when switching with valve operation.
Fluidization of the packed bed occurs, causing powdering of the adsorbent.

Conventionally, as shown in the example in Figure 2, the adsorption operation generally dehumidifies the process gas by flowing it from the top to the bottom of the packed bed, and the desorption (regeneration) operation desorbs the moisture adsorbed from the top as effectively as possible. To do this, high-temperature (regeneration) gas is flowed from the bottom to the top of the packed bed for regeneration. To switch between adsorption and desorption, open and close electromagnetic solenoid valves, air-operated valves, electric motor-driven valves, etc. at the entrance and exit at the same time, or open the valve that will be the exit side for the next operation first, and then open the large-mouth valve. Normally, valve operations are performed sequentially, and no consideration is given to the problems of fluidization and powderization of the adsorbent, which will be described later.

[Problem that the invention seeks to solve]

Molecular Sheep 3, a commonly used dehumidifier
The fluidization start speed of the % chain varies depending on the type of gas and pressure, but if the superficial velocity is 1.5 to 20117 seconds, it will also vary depending on the volume of the superficial column above and below the packed bed.
Depending on the valve operation, an upward gas flow occurs, and the number
It is expected that the fluidization phenomenon will occur for 0 seconds to several minutes.

When this fluidization occurs repeatedly, the molecular sheep is worn out and powdered, and small powders are blown up and partially deposited on the top of the packed bed, causing uneven flow and increased pressure drop in the packed bed.

Moisture absorbents weaken in strength when used repeatedly over a long period of time, cracking and powdering occur, increasing the ventilation resistance of the filled layer (
Depending on the adsorption and regeneration gas composition and temperature, impurities may accumulate in the adsorbent and the adsorption performance may deteriorate. It is customary to replace it with a new one every 2 to 6 years.

As a result of basic tests, the compressive strength of commercially available molecular sheep for dehumidification is considerably reduced by repeated adsorption and desorption operations (
A decrease of about 30% after 300°C regeneration and 50 cycles was observed, and cracks were observed on some surfaces depending on the regeneration temperature and adsorbent. However, even if the strength of the adsorbent decreases, in order to cause it to powder in the packed bed, there are generally three things that can cause it to become powder: ■ Vibration of the adsorption tower body, ■ Fluidization of the adsorbent by gas flow, and ■ Gas blowing from the gas dispersion port. Powdering is thought to occur when adsorbent fluidization occurs, such as when adsorbent fluidizes due to soaking, and once powdering occurs, gas drift occurs due to partial blockage of the packed bed by powder. It is thought that fluidization of the adsorbent occurs in areas where the gas flow rate is high, further promoting pulverization.

While pursuing the cause of this powdering, the inventor discovered that LNC)
Like a dehumidification tower in a plant, this is a system in which adsorption/desorption can be repeated by switching between two or more dehumidification towers by operating a valve.Adsorption/desorption is performed under pressure, and the operating pressures for adsorption and desorption are slightly different. In this case, due to this pressure difference, a temporary partial flow of gas (differential pressure/fluctuation) occurs within the tower depending on the valve operation.
It was discovered that it fluidizes the adsorbent and causes powdering.

The object of the present invention is to provide a method for controlling an adsorption tower that prevents fluidization and powdering of an adsorbent.

[Failure to solve the problem]

1) In an adsorption/desorption system that uses two or more adsorption towers filled with adsorbent to alternately perform adsorption and desorption operations by switching valves, both adsorption and desorption operations are carried out in the packed bed during operation. A method for controlling an adsorption tower, characterized in that the direction of gas flow in the adsorption tower is from top to bottom, and valve switching for adsorption/desorption or desorption/adsorption is performed by simultaneously opening and closing inlet and outlet valves.

2) In an adsorption/desorption system where two or more adsorption towers filled with adsorbent are used repeatedly for adsorption and desorption operations by switching valves, if the adsorption operation pressure and desorption operation pressure are different, the pressure A method for controlling an adsorption tower, which is characterized in that when switching the valves, the valve on the side where the gas flow direction through the packed bed temporarily goes from top to bottom is opened first, and the remaining valves are opened later.

The method of the present invention takes measures against the problems of fluidization and powdering of the adsorbent, as follows: 1) The gas flow in the packed bed is made to flow from top to bottom in both adsorption and desorption operations.

2) To switch the adsorption/desorption or desorption/adsorption valves, either open and close the inlet and outlet valves at the same time, or temporarily change the flow direction of the gas inside the column to an upward direction when switching the valves due to the difference between the adsorption operating pressure and the desorption operating pressure. Open the valve on the side facing downward first, then open the remaining valves.

It's a method. This can prevent fluidization of the adsorbent and prevent the above-mentioned troubles.

[Effect]

1) The piping is such that the flow direction of gas in the packed bed during both adsorption and desorption operations is from top to bottom.

Since the desorption operation is carried out using high-temperature gas at 250 to 300°C, the efficiency hardly changes whether it is from the top down or from the bottom up.

2) To switch the adsorption/desorption or desorption/adsorption valves, either open and close the inlet and outlet valves at the same time, or temporarily change the direction of the gas flow inside the column upwards due to the difference between the adsorption operating pressure and desorption operating pressure when switching the valves. Open the valve on the side facing downward first, then open the remaining valves. FIG. 1 is an illustration of a natural gas recovery and purification process to which the method of the present invention is applied. In the case of FIG. 1, the regeneration operating pressure is 1 to 3 Ky/cr lower than the adsorption operating pressure.
Since Aa is high, Vll l after the regeneration operation of adsorption tower A is completed.
When v, □, VI3, and VI4 are all switched from the closed state to the suction operation, that is, to the state shown in FIG. 1, first VI4 is opened, and then Vll is opened. Also, after the adsorption operation in adsorption tower B is completed, it becomes v2+.

V221 To switch from the quiet state of V23 and V24 to the playback operation, that is, the state shown in Figure 1, first
By opening □ and then opening V23, the temporary gas flow at the time of valve switching can be made to flow from top to bottom, and fluidization phenomenon and powdering can be prevented.

〔Example〕

Example The method of the present invention was applied to the natural gas purification equipment shown in FIG. 1 under the following operating conditions.

Operating conditions The switching valves were all globe-shaped valves driven by electric motors, and the valve opening degree and opening ratio were close to a first-order proportional relationship.

Vll and v in Figure 1, , vse, Vll and V
21 and V24゜■? 2 and V23 open and close the entrance and exit at the same time, and the closing speed is 1 by adjusting the motor reduction ratio.
By setting the opening speed to 2 minutes, stable switching operation was possible.

〔Effect of the invention〕

According to the method of the present invention, fluidization and powdering of the adsorbent can be prevented.

The present invention is applicable to the operation of adsorption towers in natural gas (LN()) recovery and purification plants, petroleum-associated gas (LP()) recovery and purification plants, CO separation and purification plants, and other chemical process gas dehumidification equipment. can.

[Brief explanation of drawings]

FIG. 1 is an illustration of a natural gas recovery and purification process to which the method of the present invention is applied, and FIG. 2 is an illustration of a natural gas recovery and purification process to which the conventional method is applied. 1... Desulfurization tower, 3... Adsorption tower, 4... Compressor, 5... Heating furnace, 6... Cooler, 7... Flash drum

Claims (1)

[Claims] 1) In an adsorption/desorption system that is repeatedly used, adsorption and desorption operations are performed alternately by switching valves between two or more adsorption towers filled with adsorbent. A method for controlling an adsorption tower, characterized in that the direction of gas flow in the packed bed during operation is from top to bottom, and valve switching for adsorption/desorption or desorption/adsorption is performed by simultaneously opening and closing inlet and outlet valves. 2) In an adsorption/desorption system where two or more adsorption towers filled with adsorbent are used repeatedly for adsorption and desorption operations by switching valves, if the adsorption operation pressure and desorption operation pressure are different, the pressure A method for controlling an adsorption tower, which is characterized in that when switching the valves, the valve on the side where the gas flow direction through the packed bed temporarily goes from top to bottom is opened first, and the remaining valves are opened later.