RU2786205C1 - Adsorbent regeneration method in natural gas processing - Google Patents

Abstract

FIELD: natural gas processing.

SUBSTANCE: invention relates to a technology for the regeneration of adsorbents in the processing of natural gas. The invention relates to a method for the regeneration of adsorbents in the processing of natural gas, includes the stages of heating the adsorbent with desorption of the adsorbate and cooling the adsorbent with flows of regenerating and cooling inert gas. As a regenerating and cooling inert gas, dry nitrogen is used, having a water dew point not higher than the required water dew point of the stream purified on the adsorbent. Dry nitrogen sequentially passes through the layer of the cooled adsorbent at the stage of cooling the adsorbent, is heated to the regeneration temperature in the recuperative heat exchanger and additional heating apparatus, is passed through the layer of the heated adsorbent at the stage of heating the adsorbent with desorption of the adsorbate, then the exhaust gas of regeneration enters together with the desorbate in the form of nitrogen desorbate mixture of non-stationary composition into a recuperative heat exchanger for heating dry nitrogen, cools in an additional cooling apparatus and is fed to equalize the composition of the nitrogen-desorbate mixture for mixing with dry nitrogen, after which it is mixed with air, sent to the reactor for the thermocatalytic oxidation of the desorbed adsorbate and then discharged onto a candle.

EFFECT: reduction of metal consumption of equipment, the amount of regeneration gas used and emissions of toxic products into the atmosphere.

18 cl, 2 dwg, 3 tbl, 1 ex

Description

The invention relates to a technology for the regeneration of adsorbents in the processing of natural gas and can be used in the gas and petrochemical industry.

One of the characteristic and costly processes of large-scale processing of natural gas is the deep purification of gaseous and liquid process streams from impurities such as water, hydrogen sulfide, sulfur compounds and hydrocarbons at installations with a fixed adsorbent bed (zeolites, silica gel, activated carbon), which, after saturation with these impurities undergoing regeneration.

There is a known method of regeneration of silica gel spent in the process of cleaning diesel fuel saturated with oxidized sulfur compounds in the form of sulfones and sulfoxides to their content of 20 mg/kg, including washing the silica gel in the adsorber with water at a temperature of 20-50 ° C, drying the washed silica gel with pumped into the adsorber with nitrogen at a temperature of 180-195 °C, removal of nitrogen containing water vapor and traces of residual hydrocarbons from the adsorber to the condenser with its cooling to 40-60 °C, then the cooled nitrogen is removed to the separator for separation of the liquid phase and its further recirculation into the adsorber to ensure that the temperature of the washed and dried silica gel is reduced to 30–40 °C (patent for invention RU 2657342, IPC B01J 20/34, filed on April 19, 2017, published on June 19, 2018). The disadvantages of the invention are:

- desorption of sulfur compounds adsorbed by silica gel by washing the adsorbent with water, that is, by replacing the adsorbed sulfur compounds with adsorbed water, followed by desorption of adsorbed water with nitrogen at 180–195 °C, which is energetically unfavorable, since the heat of water desorption is significantly higher than the heat of desorption of sulfur compounds due to the higher the affinity of silica gel for water;

- practically unrealizable cooling of silica gel to 30-40 °C using desorbing nitrogen at a temperature of 40-60 °C after condensation of water and residual hydrocarbons from it, since nitrogen cooled to a maximum of 40 °C cannot cool silica gel to 30-40 °C WITH;

- equilibrium 100% humidity of nitrogen supplied for cooling silica gel after moisture condensation in it, leading to drying of nitrogen by silica gel at the final stage of cooling and, accordingly, to a decrease in the adsorption capacity of silica gel during purification of diesel fuel from sulfur compounds.

A known method of co-purification of natural gas from the fraction of heavy hydrocarbons and sulfur-containing impurities by adsorption, while active carbon is used as the adsorbent, and the adsorption purification process is carried out in a two-phase mode with regeneration of the exhaust adsorbent with heated inert gas and a counterflow of purified natural gas passed through the exhaust adsorbent layer followed by cooling of the regenerated adsorbent by natural cooling (patent for invention RU 2465041, IPC B01D 53/14, declared on 05/04/2011, published on 10/27/2012). The disadvantages of the invention are:

- the impossibility of industrial implementation of the method, since the intensive natural cooling of the adsorbent after regeneration at high temperature cannot be ensured by heat transfer with the environment through the wall of the adsorber of large diameter;

- artificial increase in the duration of the adsorption phase due to the long regeneration phase to ensure inefficient natural cooling of the adsorbent, leading to a multiple increase in the size of the adsorber, capital and operating costs for the implementation of the process as a whole;

- shell-and-tube design of the adsorber for regeneration with the placement of the adsorbent in the tube space, leading to an increase in dimensions, metal consumption and cost of the device

Closest to the claimed invention is the method of regenerating the adsorber from moisture, including heating to 180-200 ° C and cooling the adsorber with a gas flow with the discharge of part of it into the atmosphere during heating, the use of regenerating gas - nitrogen when heated, while heating up to 180-200 ° C provided in two stages, at the first stage, the regenerating gas is heated, ejected and mixed with air to form a gas flow, which is discharged into the atmosphere after the adsorber, when the gas flow temperature reaches 100-110 ° C, the air supply is stopped, at the second stage, the gas flow is circulated through adsorber, and a part of the gas flow equal to the amount of regenerating gas supplied for ejection is discharged into the atmosphere, when 180-200 ° C is reached, heating and ejection are stopped, after which the adsorber is gradually evacuated to 1 * 10 ^-2 mm Hg. Art., while at the first stage vacuum up to 100-200 mm Hg. Art. with simultaneous supply of a calibrated flow rate of regenerating gas to the adsorber, at the second stage, evacuation is carried out using a mechanical pump, and then cooled to the operating temperature by a gas stream, which is used as a pure working gas, organizing the gas flow when the adsorber is heated to 180-200 ° C for the first stage of evacuation and during cooling is carried out by ejectors, in addition, during cooling, a part of the undried working gas is used for ejection (patent for invention RU 2239489, IPC B01D 53/96, B01J 20/34, declared 10/21/2002, published 11/10/2004 G.). The disadvantages of the invention are:

- carrying out the regeneration process in two stages in several stages with different technological operations, which complicates the process control;

- inefficient from the standpoint of heat supply in the electric heater, the formation of a coolant flow at the first stage of the first stage of regeneration by heating nitrogen to 280-300 ° C in the electric heater, to which cold air is then pumped, due to the relatively low heat transfer coefficient (low gas flow rate in the electric heater) and temperature difference;

- heating at the second stage of the first stage of regeneration of the adsorbent layer only to a temperature of 180-200 °C, which is insufficient for a high degree of restoration of the adsorption properties of sorbents, especially some types of zeolites widely used in deep drying and purification of process streams;

- the influence of fluctuations in ambient temperature on the parameters of the process, because when forming a coolant flow, air is pumped into the system from the atmosphere;

- use at two stages of the second stage of regeneration of various devices with different depths of evacuation, which significantly increases the cost of the implementation of the method;

- the ingress of hydrocarbons into the desorption products during drying of natural gas together with water, which, together with regeneration gases, are discharged into the atmosphere, polluting the environment.

When creating the invention, the task was to develop an environmentally friendly method for the regeneration of adsorbents in the processing of natural gas through the efficient use of process streams.

The problem is solved due to the fact that the method of regeneration of adsorbents in the processing of natural gas includes the stages of heating the adsorbent with desorption of the adsorbate and cooling the adsorbent with flows of regenerating and cooling inert gas, respectively, while dry nitrogen having a dew point is used as regenerating and cooling inert gas for water is not higher than the required dew point for water of the stream purified on the adsorbent, dry nitrogen sequentially passes through the layer of the cooled adsorbent at the stage of cooling the adsorbent, is heated to the regeneration temperature in the recuperative heat exchanger and additional heating apparatus, is passed through the layer of the heated adsorbent at the stage of heating adsorbent with desorption of the adsorbate, then the exhaust gas of regeneration enters together with the desorbate in the form of a nitrogen-desorbate mixture of a non-stationary composition into a recuperative heat exchanger for heating dry nitrogen, is cooled in an additional cooling apparatus ate and is fed to equalize the composition of the nitrogen-desorbate mixture for mixing with dry nitrogen, after which it is mixed with air, sent to the reactor for the thermal catalytic oxidation of the desorbed adsorbate, and then discharged onto the candle.

When using synthetic zeolites as an adsorbent, it is advisable to provide the temperature of dry nitrogen passed through the heated adsorbent layer at the adsorbent heating stage with adsorbate desorption in the range of 250–350 °C.

When using activated carbons as an adsorbent, it is advisable to ensure the temperature of dry nitrogen passed through the heated adsorbent layer at the stage of adsorbent heating with adsorbate desorption in the range of 180–250 °C.

As an additional heating device, you can use a direct heating furnace, tubular electric heaters or other heat exchangers using condensed water vapor or heat transfer oil or hot flue gases.

As an additional cooling device, you can use a water or air cooler.

When equalizing the composition of the nitrogen-desorbate mixture, it is expedient to ensure that the concentration of the oxidizable desorbed adsorbate in the mixture of the exhaust gas of regeneration with air is not higher than the value at which the temperature sintering of the catalyst begins in the reactor for the thermocatalytic oxidation of the desorbed adsorbate.

With a limited capacity range of the desorbed adsorbate thermocatalytic oxidation reactor, it is expedient to provide for the stabilization of the regeneration exhaust gas flow rate with the help of a receiver at the moment of peak release of the desorbed adsorbate. Moreover, the mixing of the regeneration exhaust gas with dry nitrogen is carried out before and/or after the receiver.

To equalize the composition of the nitrogen-desorbate mixture, it is expedient to supply the regeneration exhaust gas through an injector to a receiver with a diaphragm mixer and a regeneration gas injection circulation system.

It is advisable to provide the air flow rate supplied for mixing with the regeneration exhaust gas in an amount of at least a tenfold excess compared to the minimum air consumption required for complete oxidation of the desorbed adsorbate in the regeneration exhaust gas.

Noble metals or transition metal oxides can be used as a catalyst in the reactor for the thermal catalytic oxidation of the desorbed adsorbate.

When regenerating adsorbents for cleaning liquid-phase flows from impurities, before the stage of heating the adsorbent with desorption of the adsorbate, it is advisable to purge the adsorbent layer with dry nitrogen and collect the separated liquid phase in an additional collector with the combination of purge gases and exhaust regeneration gas.

It is expedient for a wide range of performance of the thermal catalytic oxidation reactor to provide for the supply of regeneration exhaust gas to the reactor directly without dilution with dry nitrogen.

It is advantageous to combine the regeneration exhaust gas with other natural gas processing streams that require oxidation prior to release to the atmosphere, such as acid gas from an amine treatment plant, prior to being fed into the catalytic reactor.

It is advisable if there is a natural gas denitrification plant in the natural gas processing plant as a regenerating and cooling gas to use nitrogen-containing gas produced at this plant.

The figure 1 shows a diagram of one of the possible embodiments of the claimed invention using the following notation:

1-14 - pipeline;

101-103 - adsorber;

201 - recuperative heat exchanger;

202 - additional heating apparatus;

203 - additional cooling apparatus;

301 - receiver;

401 – reactor for thermocatalytic oxidation of desorbed adsorbate.

The circuit shown in figure 1 functions as follows.

It is conventionally assumed that adsorber 101 is at the adsorption stage, adsorber 102 is at the adsorbent cooling stage, and adsorber 103 is at the adsorbent heating stage with adsorbate desorption. The flow of purified liquefied hydrocarbon gas (LHG) through the pipeline 1 enters the adsorber 101 for adsorption purification from sulfur compounds and passes the adsorbent layer from bottom to top. The LPG stream, purified from sulfur compounds, is discharged from the top of the adsorber 101 through pipeline 2 for further processing at the natural gas processing plant.

Dry nitrogen is used as a regenerating and cooling gas, which is produced at the natural gas processing plant and comes from the factory network through pipeline 3.

Dry nitrogen coming from the factory network through pipeline 3 is passed from top to bottom through a layer of cooled adsorbent in adsorber 102, which is at the stage of adsorbent cooling, and then sequentially passes through pipeline 4 a recuperative heat exchanger 201 and through pipeline 5 an additional heater 202 for heating to the regeneration temperature. The heated flow as regeneration gas is passed from top to bottom through the heated adsorbent bed in the adsorber 103, which is at the adsorbent heating stage with adsorbate desorption. The regeneration exhaust gas in the form of a nitrogen-desorbate mixture of a non-stationary composition from the adsorber 103 is sent through pipeline 7 first to the recuperative heat exchanger 201 for heating dry nitrogen, and then through pipeline 8 to an additional cooling apparatus 203 for additional cooling. The cooled nitrogen-desorbate mixture is further mixed with the flow of dry nitrogen entering through pipeline 12 to equalize the composition of the nitrogen-desorbate mixture, forming a regeneration exhaust gas stream of a stationary composition, which is then fed through pipeline 9 to the reactor for thermal catalytic oxidation of the desorbed adsorbate 401, where sulfur compounds are oxidized oxygen from the air entering through pipeline 14 and is discharged to the candle through pipeline 13. The formation of the exhaust gas flow of regeneration of the stationary composition by mixing with the dry nitrogen flow also makes it possible to avoid the temperature increase in the reactor for the thermocatalytic oxidation of the desorbed adsorbate 401.

At the time of the peak release of sulfur compounds to stabilize the flow rate of the regeneration exhaust gas supplied to the reactor for the thermal catalytic oxidation of the desorbed adsorbate 401, part of the nitrogen-desorbate mixture after the additional cooling apparatus 203 is discharged through the pipeline 10 to the receiver 301. The receiver 301 is unloaded by directing its contents through the pipeline 11 for mixing with the nitrogen-desorbate mixture coming from the additional cooler 203 to the reactor 401 through pipeline 9, during the subsequent decrease in the concentration of sulfur compounds in this stream.

A possible cyclogram of the operation of adsorbers 101-103 is shown in figure 2.

Example. Performed mathematical modeling of the method of regeneration of adsorbents in the processing of natural gas in accordance with the prototype and the claimed invention. The flow of LPG, the composition of which is shown in table 1, in the amount of 135864 kg/h is fed into the adsorber at the stage of adsorption. Purification of LPG from sulfur compounds (mercaptans) occurs at a temperature of 40 ° C and a pressure of 18.3 bar (g) to a level of 15 ppm mass. The saturated adsorbent is regenerated with dry nitrogen at a pressure of 17.3 bar (g) and a temperature of 270 °C for the proposed method and 200 °C for the prototype. For the proposed method, in contrast to the prototype, the supply of dry nitrogen is provided to maintain the required concentration of mercaptans in the exhaust gas of regeneration in the form of a nitrogen-desorbate mixture sent to the reactor for thermal catalytic oxidation of the desorbed adsorbate. According to the claimed invention, during the peak release of mercaptans (the fourth hour of the adsorbent heating stage with adsorbate desorption), the main part of the regeneration exhaust gas flow will be fed to the receiver, which allows stabilizing the regeneration exhaust gas flow entering the desorbed adsorbate thermocatalytic oxidation reactor. The material balances of both methods are shown in table 2. From the data in table 2 it can be seen that for the prototype during the period of peak release of mercaptans for their complete oxidation, a larger amount of atmospheric oxygen will be required, which causes an increase in temperature in the reactor for the thermocatalytic oxidation of the desorbed adsorbate from 460 ° C to 516 ° C. The results of calculations of adsorption and regeneration given in Table 3 also show that carrying out the regeneration of adsorbents for the proposed method at a higher temperature of 270 ° C makes it possible to increase the degree of regeneration of the adsorbent and, as a result, the capacity of the regenerated adsorbent, reducing the amount of adsorbent loaded and the metal consumption of adsorbers, i.e. e. operating and capital costs. Also, the proposed method will require a smaller amount of regeneration gas due to the fact that with an increase in the regeneration temperature of the adsorbents, the heat capacity of the regeneration gas increases. The catalytic oxidation of impurities extracted at the adsorption stage makes it possible to increase the level of environmental safety of the method by reducing emissions of toxic substances from production into the environment.

Thus, providing a reduction in the metal consumption of equipment, the amount of regeneration gas used and emissions of toxic products into the atmosphere, the claimed invention solves the problem of developing an environmentally friendly method for the regeneration of adsorbents in the processing of natural gas through the efficient use of process streams.

Claims (18)

1. A method for regenerating adsorbents in the processing of natural gas, which includes the stages of heating the adsorbent with desorption of the adsorbate and cooling the adsorbent with flows of regenerating and cooling inert gas, respectively, characterized in that dry nitrogen is used as the regenerating and cooling inert gas, having a dew point in water not higher than the required water dew point of the stream purified on the adsorbent, while dry nitrogen sequentially passes through the layer of the cooled adsorbent at the adsorbent cooling stage, is heated to the regeneration temperature in the recuperative heat exchanger and additional heating apparatus, is passed through the heated adsorbent layer at the adsorbent heating stage with adsorbate desorption, then the regeneration exhaust gas enters together with the desorbate in the form of a nitrogen-desorbate mixture of a non-stationary composition into a recuperative heat exchanger for heating dry nitrogen, is cooled in an additional cooling apparatus and is fed to leveling the composition of the nitrogen-desorbate mixture for mixing with dry nitrogen, after which it is mixed with air, sent to the reactor for the thermal catalytic oxidation of the desorbed adsorbate, and then discharged onto a candle. 2. The method according to claim 1, characterized in that the temperature of dry nitrogen passed through the layer of heated adsorbent at the stage of heating the adsorbent with desorption of the adsorbate is provided in the range of 250-350 °C. 3. The method according to claim 1, characterized in that the temperature of dry nitrogen passed through the layer of heated adsorbent at the stage of heating the adsorbent with desorption of the adsorbate is provided in the range of 180-250 °C. 4. The method according to claim 1, characterized in that a direct heating furnace is used as an additional heating apparatus. 5. The method according to p. 1, characterized in that tubular electric heaters are used as an additional heating apparatus. 6. The method according to p. 1, characterized in that the additional heating apparatus uses condensed water vapor or heat transfer oil or hot flue gases. 7. The method according to p. 1, characterized in that a water or air cooler is used as an additional cooling device. 8. The method according to claim 1, characterized in that when leveling the composition of the nitrogen-desorbate mixture, the concentration of the oxidizable desorbed adsorbate in the mixture of the exhaust gas of regeneration with air is provided not higher than the value at which temperature sintering of the catalyst begins in the reactor for the thermocatalytic oxidation of the desorbed adsorbate. 9. The method according to p. 1, characterized in that the flow rate of the exhaust gas of regeneration is stabilized using a receiver. 10. The method according to claim 9, characterized in that the regeneration exhaust gas is mixed with dry nitrogen before and/or after the receiver. 11. The method according to claim 1, characterized in that the regeneration exhaust gas is fed through an injector into a receiver with a diaphragm mixer and a regeneration gas injection circulation system. 12. The method according to claim 1, characterized in that the flow rate of air supplied for mixing with the regeneration exhaust gas is provided in an amount of at least a tenfold excess compared to the minimum air flow required for complete oxidation of the desorbed adsorbate in the regeneration exhaust gas. 13. The method according to claim 1, characterized in that noble metals are used as a catalyst in the reactor for the thermal catalytic oxidation of the desorbed adsorbate. 14. The method according to p. 1, characterized in that transition metal oxides are used as a catalyst in the reactor for the thermal catalytic oxidation of the desorbed adsorbate. 15. The method according to claim 1, characterized in that before the stage of heating the adsorbent with desorption of the adsorbate, the adsorbent layer is purged with dry nitrogen and the separated liquid phase is collected in an additional collector with the combination of purge gases and exhaust regeneration gas. 16. The method according to p. 1, characterized in that the regeneration exhaust gas after the additional cooling apparatus is sent directly to the thermocatalytic oxidation reactor. 17. The method according to claim 16, characterized in that the exhaust gas of regeneration before the thermocatalytic reactor is combined with other utilized streams of the natural gas processing plant. 18. The method according to claim 1, characterized in that the regenerating and cooling gas is produced at the natural gas denitrification plant of the natural gas processing plant.

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