APPARATUS AND PROCESS FOR PRODUCING A DEACIDIFIED FLUID STREAM

Abstract

A process for producing a deacidified fluid stream from a fluid stream comprising methanol and at least one acid gas, comprising a) an absorption step in which the fluid stream is contacted with an absorbent in an absorber to obtain an absorbent laden with methanol and acid gases and an least partly deacidified fluid stream; b) a regeneration step in which at least a portion of the laden absorbent obtained from step a) is regenerated in a regenerator to obtain an at least partly regenerated absorbent and a gaseous stream comprising methanol, water and at least one acid gas; c) a recycling step in which at least a substream of the regenerated absorbent from step b) is recycled into the absorption step a); d) a condensation step in which a condensate comprising methanol and water is condensed out of the gaseous stream from step b); e) a distillation step in which at least a portion of the condensate from step d) is guided into a distillation column to obtain a top stream comprising methanol and a bottom stream comprising water;

which comprises recycling at least a portion of the bottom stream from step e) into the regenerator.

An apparatus for deacidifying a fluid stream, comprising methanol and at least one acid gas, according to claim 1, comprising a) an absorber comprising an absorption zone, at least one feed for absorbent, a feed for the fluid stream to be deacidified, a liquid draw for the laden absorbent, a draw point for the deacidified fluid stream and optionally a rescrubbing zone with a feed for scrubbing agent; b) a regenerator comprising a regeneration zone, an evaporator, a feed for the laden absorbent, a liquid draw in the bottom of the regenerator and a gas draw in the top region of the regenerator; c) at least one top condenser connected to the gas draw of the regenerator, comprising a gas draw and a condensate outlet; and d) a distillation column comprising a condenser, an evaporator, a feed for the condensate outlet of the top condenser, a vapor draw in the top region of the column and a liquid draw at the bottom of the distillation column,

wherein the regenerator has a feed connected to the liquid draw at the bottom of the distillation column.

Claims

1.-15. (canceled)

16. A process for producing a deacidified fluid stream from a fluid stream comprising methanol and at least one acid gas, comprising a) an absorption step in which the fluid stream is contacted with an absorbent in an absorber to obtain an absorbent laden with methanol and acid gases and an at least partly deacidified fluid stream; b) a regeneration step in which at least a portion of the laden absorbent obtained from step a) is regenerated in a regenerator to obtain an at least partly regenerated absorbent and a gaseous stream comprising methanol, water and at least one acid gas; c) a recycling step in which at least a substream of the regenerated absorbent from step b) is recycled into the absorption step a); d) a condensation step in which a condensate comprising methanol and water is condensed out of the gaseous stream from step b); e) a distillation step in which at least a portion of the condensate from step d) is guided into a distillation column to obtain a top stream comprising methanol and a bottom stream comprising water; which comprises recycling at least a portion of the bottom stream from step e) into the regenerator.

17. The process according to claim 16, wherein the fluid stream introduced into the process comprises methanol in the range from 50 to 5000 ppmv.

18. The process according to claim 16, wherein the fluid stream introduced into the process comprises hydrocarbons and the hydrocarbons introduced into the process comprise in the range from 90% to 99.5% by volume of methane, and/or wherein the fluid stream introduced into the process comprises acid gases in the range from 0.01% to 40% by volume.

19. The process according to claim 16, wherein an additional expansion step is conducted between absorption step a) and regeneration step b).

20. The process according to claim 16, wherein 50% to 100% by volume of the bottom stream from step e) is recycled into the regenerator.

21. The process according to claim 16, wherein the at least a portion of the bottom stream from step e) is recycled into the upper region or above the regeneration zone of the regenerator in step b), or wherein the regenerator in step b) comprises a regeneration zone and a rescrubbing zone and the laden absorbent is introduced between regeneration zone and rescrubbing zone and at least a portion of the bottom stream from step e) is recycled into the upper region or above the rescrubbing zone.

22. The process according to claim 16, wherein the pressure at the top of the distillation column in step e) is in the range from 1 to 3 bar.

23. The process according to claim 16, wherein the distillation column in step e) has 3 to 25 plates.

24. The process according to claim 16, wherein the distillate obtained in the condenser of the distillation column in step e) is recycled to an extent of more than 50% by volume as reflux to the distillation column.

25. The process according to claim 16, wherein the condensation step d) comprises at least two condensers, the first condenser being cooled with air or cooling water and the second condenser being cooled with a coolant.

26. The process according to at claim 21, wherein the rescrubbing zone of the regenerator has trays or random packings or structured packings, and the number of trays is in the range from 1 to 10 trays or the height of the random packings/structured packings is in the range from 1 to 10 m.

27. The process according to claim 16, wherein the absorbent is an aqueous absorbent.

28. The process according to claim 16, wherein one or more of the following workup steps are performed on the deacidified fluid stream from step a): aa) dewatering; bb) removal of mercury; cc) removal of nitrogen; dd) removal of natural gas condensates; and/or ee) liquefaction.

29. An apparatus for deacidifying a fluid stream, comprising methanol and at least one acid gas, according to claim 16, comprising a) an absorber comprising an absorption zone, at least one feed for absorbent, a feed for the fluid stream to be deacidified, a liquid draw for the laden absorbent, a draw point for the deacidified fluid stream and optionally a rescrubbing zone with a feed for scrubbing agent; b) a regenerator comprising a regeneration zone, an evaporator, a feed for the laden absorbent, a liquid draw in the bottom of the regenerator and a gas draw in the top region of the regenerator; c) at least one top condenser connected to the gas draw of the regenerator, comprising a gas draw and a condensate outlet; and d) a distillation column comprising a condenser, an evaporator, a feed for the condensate outlet of the top condenser, a vapor draw in the top region of the column and a liquid draw at the bottom of the distillation column, wherein the regenerator has a feed connected to the liquid draw at the bottom of the distillation column.

30. The use of an apparatus according to claim 29 for production of deacidified natural gas having a low methanol content.

Description

EXAMPLES

[0333] The invention is illustrated by the following examples:

[0334] The examples are based on calculations performed using a simulation model. The phase equilibria were described using a model by Pitzer (K. S. Pitzer, Activity Coefficients in Electrolyte Solutions 2nd ed., CRC Press, 1991, Chapter 3, Ion Interaction Approach: Theory). The simulation of the absorption processes is described by means of a mass transfer-based approach; details of this are given in Asprion (Asprion, N.: Nonequilibrium Rate-Based Simulation of Reactive Systems: Simulation Model, Heat Transfer, and Influence of Film Discretization, Ind. Eng. Chem. Res. (2006) 45 (6), 2054-2069). The distillation column was designed by means of a thermodynamic model based on the NRTL approach for the description of the vapor-liquid equilibrium of water-methanol.

[0335] All pressures reported in the present document are absolute pressures.

[0336] In the present document m.sup.3 (STP)/h is the volume flow rate reported in standard cubic meters per hour. A standard cubic meter is based on a temperature of 273.15 K and a pressure of 1.01325 bar. All values reported in the unit % by volume are likewise based on these conditions.

[0337] The following process conditions were assumed for all examples: [0338] Feed gas: 1.0% by volume of CO.sub.2, 520 ppmv of methanol, balance: hydrocarbons (CH.sub.4, C.sub.2H.sub.6), at a temperature of 26 C. and a pressure of 63.5 bar. [0339] Absorbent: [0340] An amine solution consisting of piperazine and methyldiethanolamine with a total amine content of 40% by weight. 0.24 m.sup.3/h of regenerated absorbent is used for every 1000 m.sup.3 (STP)/hr of feed gas. The regenerated absorbent has a temperature of 35 C. [0341] The internals in the absorption column are random packings having a total bed height of 14 m. [0342] In the regenerator, random packings are likewise used for the regeneration zone, with a bed height of 10 m. The regenerator is operated at a pressure of 1.5 bar. [0343] The distillation column is operated at a pressure of 1.25 bar. In the simulation, the column is modeled by means of 10 theoretical plates. The feed is at the 6th plate counted from the bottom.

[0344] All examples have to fulfill the same separation task defined in the following specifications: [0345] The methanol content of the deacidified fluid stream (natural gas) which is obtained at the top of the absorber is not to exceed a value of 1 ppmv. [0346] The CO.sub.2 content of the deacidified fluid stream (natural gas) which is obtained at the top of the absorber is not to exceed a value of 15 ppmv. [0347] The methanol recovered at the top of the methanol distillation is to have a purity of greater than 96% by weight.

[0348] Only the difference with regard to distillation step e) will be discussed hereinafter since no significant differences arise with regard to the essential operating parameters in the absorption, regeneration, condensation and recycling steps a) to d).

Example 1

[0349] A process is simulated in a plant according to FIG. 1. The process consists of an absorption column, an expansion vessel (HP flash), regenerator with evaporator, and top condenser. The liquid stream (methanol+water) condensed out in the top condenser is fed through a heat exchanger in a further column. Methanol (top product) and water (bottom product) are separated here by distillation. The bottom product is returned to the top of the regenerator.

[0350] The reflux ratio v of the distillation column is 7.5.

[0351] The methanol recovery is 90% based on the amount present fluid stream introduced into stage a).

Example 2

[0352] A process is simulated in a plant according to FIG. 2. The configuration corresponds very substantially to example 1, except that a rescrubbing section with three trays was additionally included in the regenerator.

[0353] All further components and also the process conditions are unchanged compared to example 1. The inclusion of the rescrubbing zone in the regenerator, with equal evaporator output supplied for the regenerator and also the methanol distillation, likewise leads to a methanol recovery of 90%. The rescrubbing section allows the amine content in the condenser of the regenerator and hence in the distillation section to be reduced; as well as the amines dissolved in the gas, possible droplet entrainment through the rescrubbing section is also reduced.

Comparative Example 1

[0354] Based on patent application RU2602908, a further simulation for a process was created according to FIG. 3. The crude gas stream to be purified is identical to the two examples detailed above; the apparatus sizes and evaporator outputs used (regenerator and distillation) were also kept constant. The essential difference lies in the recycling of the water from the methanol distillation directly to the top of the absorption column, and not, as before, to the top of the regenerator. Given the same number of plates and evaporator output in the methanol column, it is no longer possible with this configuration to achieve the desired methanol content (<1 ppmv) in the purified natural gas. The residual methanol content is 27 ppmv. In other words, in order to achieve the same removal of methanol, it would be necessary to use a distillation column having more plates and/or higher evaporator output.