WO2012034662A1

WO2012034662A1 - Method for cleaning up process condensate

Info

Publication number: WO2012034662A1
Application number: PCT/EP2011/004483
Authority: WO
Inventors: Carsten Taube; Michael Reinke; Christian Thaller
Original assignee: Linde Aktiengesellschaft
Priority date: 2010-09-16
Filing date: 2011-09-06
Publication date: 2012-03-22
Also published as: DE102010045587A1

Abstract

The invention relates to a method for cleaning up process condensate (10) which occurs in the steam reforming or steam cracking of hydrocarbons. In order to separate off contaminants, the process gas (10) is subjected to catalytic oxidation (R) and ion exchange (S).

Description

description

Process for the purification of process condensate

The invention relates to a process for the purification of process condensate obtained during steam reforming or steam cracking of hydrocarbons.

In steam reforming, a hydrocarbon-containing feed, such as natural gas, light gasoline or naphtha, is mixed with process steam and reacted in a reactor with catalytic assistance to a synthesis gas consisting predominantly of hydrogen and carbon monoxide. From the synthesis gas are subsequently by cooling, cleaning and decomposition products, such as

Hydrogen, carbon monoxide or oxo gas (a defined mixture of hydrogen and carbon monoxide) won. In order to suppress soot formation, it is usually necessary to reform with a larger amount of steam

as stoichiometrically necessary, so that the resulting synthesis gas contains water vapor. To separate this, the synthesis gas is cooled to below the dew point, whereby the water vapor condenses out and so-called.

Process condensate is formed. Process condensate consists for the most part of water, but also contains a variety of different

Impurities, such as alcohols, carboxylic acids, cations (Na ⁺ , Ca ²⁺ , Fe ²⁷³ *, NH ₄ \ ...), anions (N0 ₃ ^" , N0 ₂ ^" , C0 ₃ ^{2 "} , HC0 ₃ ^' , ... ) as well as dissolved gases and solids.

Process condensate also accumulates in the vapor cracking of hydrocarbons. In this case, hydrocarbon-containing inserts, such as naphtha, ethane, propane, butane, gas oil or Hydrorowachse, are cleaved in the presence of water vapor, wherein a product gas is formed, which consists primarily of hydrogen, methane, ethylene and propylene. To prevent the short-chain fission products from aggregating, the vapor cracking also becomes excessive

Steam is carried out, which is subsequently condensed out of the product gas to form process condensate. In addition to water as the main constituent, a process condensate accumulating during steam cracking contains many different substances

Impurities, such as uncleaved hydrocarbons and aromatic

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The process condensate is mixed with demineralized water, which is added to the

Process is supplied from the outside. It is then degassed and warmed against cooled process streams, evaporated and superheated, forming steam that is contaminated with impurities contained in the process condensate. The purity of this vapor is sufficiently high to keep it within the

Steam reforming or steam splitting to use as process steam. Usually, not all of the heat available in the process is needed for process steam production, so that export steam can also be produced and delivered against credit to external consumers. As the amount of the credit increases with the purity of the export steam, the aim is to produce export steam with the highest possible purity. The highest credit is for export steam that is suitable for use in a steam turbine. To do this, it must meet strict purity requirements that can not usually be met by steam produced from contaminated process condensate without an additional purification step.

In the patent application DE102006019100 a steam reformer with two independent steam systems is proposed in which process steam and

Export steam can be generated independently. While

Process steam is obtained from a mixture of untreated process condensate and demineralized water, only demineralized water is used to produce export steam. With this method, it is thus possible to produce extremely pure export steam without an additional purification step. However, a disadvantage is the high expenditure on equipment for the second steam system, the cost of steam reforming considerably

impaired.

The present invention is therefore based on the object to provide a method of the type mentioned, by which the disadvantages of the prior art can be overcome.

The stated object is achieved in that the

Process condensate of a catalytic oxidation and a itself

subjected to subsequent ion exchange. Catalytic oxidation has been the art for years and known to those skilled in the art as a process for removing organic compounds from aqueous solutions. The aqueous solution is treated with an oxidizing agent, such as. B.

Hydrogen peroxide, mixed and passed through a fixed bed catalyst. The organic compounds are oxidized here with catalytic support, in particular carbon dioxide and water.

In the inventive purification of process condensate, the catalytic oxidation is primarily used to convert alcohols - especially methanol and ethanol - and carboxylic acids to carbon dioxide and water and thereby remove. The oxidizing agent used is preferably hydrogen peroxide, which is metered into the process condensate to be purified.

In order to remove ions already present prior to the catalytic oxidation or formed during the catalytic oxidation from the process condensate, downstream treatment is followed by ion exchange. Since the ions can be both anions and cations, an expedient embodiment of the process according to the invention provides that the ion exchange is carried out in a mixed-bed ion exchanger, wherein anions and cations are simultaneously removed from the process condensate.

Often, process condensate contains cations in a concentration that is at the

Carrying out a catalytic oxidation can lead to disturbances. Thus, e.g. a process condensate obtained in steam reforming and a subsequent water gas shift, in particular ammonium ions, in an amount which does not allow its direct treatment by catalytic oxidation for economic reasons. A preferred embodiment of the method according to the invention therefore provides that the process condensate is treated by cation exchange before the catalytic oxidation for the separation of cations. For process engineering reasons, process condensate often contains solid particles which can be deposited in the apparatuses used for ion exchange and catalytic oxidation and can lead to disturbances. The invention

Therefore, the method provides a purification step which is expediently arranged before the cation exchange and / or the catalytic oxidation, in which solids are separated off from the process condensate. The inventive method can be used for the purification of any process condensate, which in the steam reforming or

Steam splitting of hydrocarbons is obtained. Preferably, however, it is used for the purification of process condensate, which in the drying of a

Process gas is obtained, which is obtained by steam reforming and subsequent water gas shift.

The process condensate purified by means of the process according to the invention can be used for the production of export steam and / or process steam.

Expediently, waste heat arising in the respective process is used for this purpose. In order to compensate for in-process water losses and to provide a sufficient amount of water for the steam generation, demineralized water is usually supplied from the outside and mixed with the purified process condensate before it is converted by the waste heat to export steam and / or process steam.

The export steam produced according to the invention can be used for a variety of applications. With particular benefit, it is used in a steam turbine process in which its energy is converted into mechanical and / or electrical energy.

The present invention offers a number of advantages. Thus, it allows a process condensate obtained during steam reforming or steam cracking to be cleaned to such an extent that steam obtained from it meets high purity requirements and can also be used in a steam turbine. To carry out the

Method required devices are relatively easy to operate and require investment costs, which are low compared to the prior art. The

proposed process steps can at typical temperatures of a

Process condensate can be performed. At most, it needs smaller

Temperature decreases, so that the cost of the temperature adjustment of the process condensate is low or equal to zero.

In the following, the invention will be explained in more detail with reference to two schematically illustrated in Figures 1 and 2 embodiments. Figure 1 shows an embodiment of the method according to the invention for the purification of a resulting in the steam reforming of hydrocarbons

Process condensate. FIG. 2 shows an embodiment of the method according to the invention with an optional pretreatment of the process condensate.

1 shows a reformer A with a combustion chamber B and a flue gas system C is shown, which is fired by burner D, where a fuel 1 and in the

Heat exchanger E1 preheated combustion air 2 are supplied. The flue gases generated by the burner D give off part of their sensible heat to the reformer tubes F containing a catalytically active material before they are removed via the flue gas system C. In the flue gas system C are several

Heat exchangers E1, E2 and E3 arranged over which the flue gases further heat is removed so that they reach the chimney J with a temperature of about 200 ° C via line 3 and the blower G. A hydrocarbon-containing insert 4 preheated in the heat exchanger E4 is mixed with process steam 5 before it is introduced into the heat exchanger E3 arranged in the flue gas system C of the reformer A and is further superheated there. In this case, the process steam 5 is metered in more than stoichiometrically in order to suppress the formation of soot in the subsequent steam reforming reaction. Via line 6, the hydrocarbon / Darrrpf mixture is withdrawn from the superheated E3 and distributed to the reformer tubes F, where they are converted with catalytic support to the process gas 7. The process gas 7, which leaves the reformer A, is cooled in the heat exchangers E5, E6, E4 and E7 to below the dew point, so that excess water vapor condenses out and forms a multiphase flow 8, which is introduced into the separator K. Here the stream 8 is in the predominantly consisting of hydrogen and carbon monoxide synthesis gas 9 and the predominantly made of water,

Contaminated process condensate 10 separated. While that

Synthesis gas 9 further treatment steps, not shown, the process condensate 10 enters the cleaning section L, in which the

Impurities are largely separated, sö that can be deducted via line 1 1 of high purity water. To compensate for unavoidable losses, demineralized water 12 is supplied from beyond the plant boundaries and into the deaerator together with the purified process condensate 11 M initiated. The degassed in the Deaerator M water 13 is preheated in the heat exchanger E7 - against the process gas to be cooled and introduced into the steam drum N. Hot water is taken ^• 14 and evaporated in heat exchanger E5 against abzukühlendes process gas 7 from the steam drum. The thus generated steam 15 is returned to the steam drum N. Via line 16 of the steam drum N steam is removed and overheated in the heat exchanger E2. Part 18 of the overheated

Steam stream 17 is delivered as export steam to an external customer (not shown), while the remainder is admixed to the insert 4 as process steam 5. FIG. 2 shows an embodiment of the cleaning section L in which

Process condensate 10 is freed of impurities. The process condensate 10, which typically has a temperature of about 70 ° C, is passed through a solid filter O in a first cleaning step to solid particles, such as

Catalyst abrasion or corrosion products, separate. The purified solids process condensate 21 is introduced into the cation exchanger P below, in the present as cations impurities such as Na ^+, Ca ² \ Fe ²¹³ * or NH ₄ ⁺ are separated. The aqueous solution 22 obtained in this process, which still contains organic impurities, in particular methanol, as well as anions, is subsequently fed to a catalytic oxidation R. Here, the organic contaminants become water with catalytic support

Implemented carbon dioxide, wherein hydrogen peroxide 23 serves as an oxidizing agent and sodium hydroxide solution 24 is added to adjust the pH. The generated material stream 25 still contains impurities, which, however, practical

exist exclusively in ionic form. In order to separate them, the stream 25 is introduced into the mixed bed toner exchanger S, where both anions, such as N0 ₃ ^" , N0 ₂ ^" , C0 ₃ ^{2 "} or HC0 ₃ ^~ , as well as cations - formed in the previous purification step R or in the cation exchanger P not separated - are removed, so that high-purity water is generated, which leaves the cleaning section L as purified process condensate 11.

Claims

claims

A process for the purification of process condensate (10) resulting from steam reforming or vapor cracking of hydrocarbons, characterized in that the process condensate (10) is subjected to catalytic oxidation (R) and subsequent ion exchange (S).

2. The method according to claim 1, characterized in that the

ion exchange process (S) is carried out in a mixed bed ion exchanger.

3. The method according to any one of claims 1 or 2, characterized in that the process condensate (10) before the catalytic oxidation (R) by

Cation exchange (P) is treated.

4. The method according to any one of claims 1 to 3, characterized in that it comprises a purification step (O), in which solids from the

Process condensate (10) are separated.

5. The method according to any one of claims 1 to 4, characterized in that the process condensate is obtained in the drying of a process gas generated by water gas shift from a steam reforming

Process gas is obtained.

6. The method according to any one of claims 1 to 5, characterized in that purified process condensate (1 1) is used to generate water vapor, as export steam (18) to a consumer outside the

Steam reforming or steam cracking process is delivered.

7. The method according to claim 6, characterized in that the export steam (18) is used in a steam turbine process.

Process according to any one of Claims 1 to 7, characterized in that purified process condensate (11) is used to produce steam used as process steam (5) within the steam reforming or steam cracking process.