WO2018068897A1 - Method and system for cleaning a gas, comprising a stripping unit operated by nitrogen - Google Patents

Abstract

The invention relates to a method for cleaning a gas, wherein undesired components are washed out of the gas by means of a washing medium in a gas washing unit (200), wherein the undesired components are driven out of the washing medium at least in part using nitrogen (b) as a stripping gas in a stripping unit (210), and wherein the nitrogen (b, f) is cooled before the nitrogen is supplied to the stripping unit (210). The invention further relates to a system for cleaning a gas.

Description

 description

 METHOD AND APPARATUS FOR CLEANING A GAS COMPRISING A NITROGEN STRIPPING UNIT

The invention relates to a method and a system for purifying a gas according to the preambles of the independent claims.

State of the art

For very different applications, pure to high purity gases are needed. For this purpose, a corresponding gas cleaned by means of appropriate equipment or

getting washed. An example of this is the so-called rectisol process, in which a Rectisol wash or in a Rectisol washing unit (English: "Rectisol Washing Unit" or RWU) with an organic detergent, for example by means of methanol as a washing medium, unwanted components are washed out of a gas. In the example of the Rectisol method, the

components to be washed out usually to acid gases such as hydrogen sulfide (H ₂ S) and carbon dioxide (C0 ₂ ), possibly also hydrogen cyanide or hydrogen cyanide (HCN) and / or carbonylsulfide (COS).

Hereinafter, a "gas" is understood to mean a pure gas or gas mixture, for example so-called synthesis gas, ie a mixture of (at least predominantly) carbon monoxide, hydrogen and possibly carbon dioxide. If "nitrogen" is mentioned below, it may be pure nitrogen or a nitrogen-rich gas mixture with, for example, more than 80, 90, 95 or 99 mol% of nitrogen. Within the Rectisol scrubbing (or another gas scrubbing unit), nitrogen (N ₂ ) can now also be used as stripping gas in a stripping column in order to expel the components now dissolved in the scrubbing medium (methanol). For this purpose, nitrogen is usually supplied at ambient temperature to the Rectisol wash and supplied to this. The pressure of the nitrogen at the plant boundary should be sufficient to be able to promote the nitrogen in the local stripping unit or stripping. Since in normal operation of the Rectisol scrubbing the amount of nitrogen is already regulated by a turbine nozzle, eliminating a flow control valve. There should be only a flap as a tight shut-off device for the standstill, which is fully open in normal operation and thus causes almost no pressure loss. The stripping column can then be operated at about 2 to 2.5 bar and a pressure for the nitrogen at the line limit of 2.1 to 2.6 bar bar is sufficient. However, depending on the pressure losses on the way from the plant boundary to the stuffer unit, the required pressure can also be higher. A separate

However, pressure increase is not required. It should be noted that the pressures used here and below are absolute pressures. If, however, the nitrogen is also used for an adsorption plant for gas purification before it is introduced into the rectisol wash, a correspondingly higher system boundary pressure of approximately 2.6 bar to 3.6 bar may be necessary. However, lower or higher pressures are also conceivable. Provision of the nitrogen can now, for example, by means of a

 Air Separation Unit (ASU). The production of air products in the liquid or gaseous state by cryogenic separation of air in air separation plants is known and, for example, H.-W. Häring (ed.), Industrial Gas Processing, Wiley-VCH, 2006, especially Section 2.2.5, "Cryogenic Rectification".

Air separation plants include distillation column systems, including, for example, two or three column arrangements for providing nitrogen-rich and oxygen-rich air products. Typically, at least one so-called (high) pressure column and a so-called low pressure column are present. The operating pressure of the high pressure column is usually 4.9 to 6.9 bar, for example, about 5.3 bar. The low-pressure column is operated at an operating pressure of usually 1, 3 to 1, 7 bar, for example, about 1, 4 bar. The stated pressure values are present in the bottom of corresponding columns. Both rectification columns can also be designed in two parts. For details refer to the literature.

The classic air separation process with the double-column process allows the removal of a certain amount of nitrogen at the top of the high-pressure column. This nitrogen stream can be obtained after heating in a heat exchanger either directly with its pressure of, for example, about 5 bar or further compressed. A nitrogen which is necessary for the mentioned rectisol process is generally supplied with the pressure of the high-pressure column and at approximately ambient temperature for rectisol washing. Against this background, the object of the present invention is to provide an improved and, in particular, more energy-efficient way of purifying gas.

Disclosure of the invention

This object is achieved by a method and a plant for cleaning gas with the features of the independent claims. Embodiments are the subject of the dependent claims and the following description. Advantages of the invention

The present invention is based on a per se known method for the purification of gas or a system for the purification of gas, as has been explained in more detail in the introduction with reference to the Rectisol method. Although reference is made here and below in particular to the Rectisol process or a Rectisol scrubbing with methanol as the scrubbing medium, the invention can also be used in other processes or plants for the purification of gas in which nitrogen is used as the stripping gas Components are expelled from the washing medium. In the case of the Rectisol process, the undesired components which are washed out of the gas by means of the washing medium, for example methanol, may be, in particular, acid gases such as hydrogen sulphide (H ₂ S) and carbon dioxide (C0 ₂ ), but also hydrocyanic acid or hydrogen peroxide Hydrogen cyanide (HCN) and / or Carbonylsuflid (COS) act, so that the gas can then be used, for example, as a synthesis gas. Subsequently, these undesirable components, at least partially, expelled from the nitrogen to continue to use the nitrogen or to be able to deliver to the atmosphere. On the known operation of a Rectisol wash or the Rectisol process should not be discussed in detail at this point. According to the invention, the nitrogen is now cooled before it is fed to the stripping column of the gas scrubbing unit (that is, for example, the recitesol scrubbing unit).

For this purpose, a suitable cooling device can be provided, through which the nitrogen is passed before it is fed to the stripping unit (or stripping column).

The invention thus allows a comparison to the initially described method, according to which the nitrogen is simply used at ambient temperature, a significant reduction of the cooling capacity for the gas-laundry unit.

As also explained below with reference to Figure 2, for example, an absorber of a corresponding gas scrubber unit is cooled to provide improved absorption by the absorbent used (in the Rectisol process

Methanol). Additional cooling can also take place elsewhere, for example in order to extract heat from the gas or detergent streams to be cleaned.

By now, however, the nitrogen is cooled before being fed to the gas scrubber unit, the additional cooling required in the gas scrubber unit is significantly reduced. An energy required for the cooling of the nitrogen is less than the energy otherwise required for the cooling of the gas-washing unit, especially since valuable peak cold is lost there.

The temperature range at which the nitrogen is cooled is preferably from 0 to -100 ° C, especially from -10 to -90 ° C, for example from -20 to -80 ° C. Particularly preferred are temperatures down to -45 or -50 ° C. For temperatures below about -45 ° (at a pressure of gaseous nitrogen of about 5 bar) can also be one or more turbine booster (compressor) for recompression of the

Turbine flow before relaxation be necessary. As exemplary temperatures to which or under which the nitrogen is cooled, are preferably -30 ° C, more preferably -50 ° C or -70 ° C, into consideration. Compared to the use of nitrogen at ambient temperature, ie at about 25 ° C, a saving of energy of, for example, 5% and more is possible with the given exemplary temperatures. Depending on the interconnection, even significantly higher savings can be achieved. For cooling the nitrogen, for example, a heat exchanger can be used for this purpose. Particularly preferably, an expansion turbine is used to cool the nitrogen, through which the nitrogen is passed. At the same time, such an expansion turbine has several advantages that can be utilized. In addition to the cooling, the nitrogen is additionally expanded, ie the pressure of the nitrogen is reduced. As mentioned above, this is usually necessary anyway in the purification of gas. While the use of pressure reduction valves uselessly depletes the energy contained in the nitrogen, the expansion turbine offers the opportunity to recuperate the energy that the nitrogen releases through expansion in the form of work. Duch the use of an expansion turbine so not only reduces the energy for cooling the gas-laundry unit due to the cooling of the nitrogen, but at the same time the energy released in the cooling of the nitrogen energy to be recovered. This recovered energy can then preferably be fed back into an energy system such as a power grid to which the gas scrubber unit is connected. However, it is also expedient to use this energy additionally or alternatively to drive at least one device such as pumps, compressors or boosters, for example, in the gas-laundry unit itself.

When using the expansion turbine, it is expedient if the nitrogen to a pressure between 2.1 bar and 2.6 bar, or if a use of the

 Nitrogen is provided for an adsorption, is relaxed between 2.6 bar and 3.6 bar. As mentioned above, these pressure ranges are those areas which nitrogen should have when used as a stripping gas, so that it can be used as efficiently as possible in the gas scrubbing unit. Thus, if the nitrogen is already correspondingly expanded by the expansion turbine, no further pressure reduction by means of a valve or the like is necessary, in which the released energy of the nitrogen would be lost unused.

Furthermore, it is advantageous when using the expansion turbine, if additional nitrogen, which should not be supplied to the gas scrubber unit, also cooled by the expansion turbine and at the same time relaxed. By thus larger amount of nitrogen, a higher cooling capacity can be achieved, which in turn leads to an energy saving in the cooling of the gas-laundry unit. Such additional nitrogen may, for example, be nitrogen which is in a Plant network is available and is not further bent or anyway to be relaxed or cooled.

Another preferred way to further cool the nitrogen is to increase a pressure of the nitrogen by means of a compressor before it is cooled by the expansion turbine. With the larger pressure gradient through the expansion is accompanied by a stronger cooling of the nitrogen. This procedure is particularly expedient if a partial nitrogen flow for any other application is anyway required at a higher pressure than present. In this case, the then necessary energy for compression can be at least partially recovered, since the energy required for the cooling of the gas-laundry unit is further reduced.

Preferably, the nitrogen supplied to the gas scrubber unit is recovered in an air separation plant. This is a typical variant to provide nitrogen for a gas scrubber unit. A structure of a corresponding system with an air separation plant, a cooling device and a gas-washing unit then looks like that the pressure nitrogen, which is provided by the air separation plant, first in the cooling device, so for example, the expansion turbine passed and then the stripping the gas-laundry unit is supplied.

The invention will be explained in more detail with reference to the accompanying drawing showing various parts of the system, by means of which the

inventive measures are explained.

Brief description of the drawing shows an air separation plant in the form of a schematic

 Process flow diagram.

Figure 2 shows a Rectisol wash unit in the form of a schematic

 Process flow diagram.

FIG. 3 shows a plant according to an embodiment of the invention in FIG

schematic representation. Figure 4 shows a system according to another embodiment of the invention in a schematic representation. Detailed description of the drawing

FIG. 1 shows an air separation plant of a type known per se, with which nitrogen can be provided for a gas scrubbing unit according to an embodiment of the invention.

Air separation plants of the type shown are often described elsewhere, for example in H.-W. Haring (ed.), Industrial Gases Processing, Wiley-VCH, 2006, especially Section 2.2.5, "Cryogenic Rectification". For detailed

Explanations on structure and mode of operation is therefore on appropriate

Reference literature referenced. An air separation plant for use of the present invention can be designed in many different ways.

The air separation plant 100 shown in FIG. 1 has, inter alia, a main air compressor 1, a pre-cooler 2, a cleaning system 3, a

Nachverdichteranordnung 4, a main heat exchanger 5, an expansion turbine 6, a throttle device 7, a pump 8 and a distillation column system 10. The distillation column system 10 comprises in the example shown a classic double column arrangement of a high pressure column 1 1 and a low pressure column 12 and a crude argon column 13 and a pure argon column 14th ,

From the main heat exchanger 5 in addition to a flow a with high pressure oxygen (PGOX), a stream b with high pressure nitrogen (PGAN) from the high pressure column 1 1 and a stream c with low pressure nitrogen (GAN) from the low pressure column 12th The pressure of the stream b is approximately at 5 bar and can then be fed to an expansion stub and then to a gas-washing unit (or rectisol wash), as will be explained below.

In Figure 2 a Rectisol-laundry is known per se, with the means of a washing medium, for example methanol, a gas according to a

Embodiment of the invention can be cleaned. The rectisol scrubber 200 comprises a heat exchanger 201, via which a gas with the stream e with scrubbing medium (stream h) is fed to an absorber 203 with a cooling unit 204. Purified gas (stream g) exits the rectisol wash via heat exchanger 201 (for use, for example, as synthesis gas).

In the Rectisol wash, a stripping unit or a stripping column 210 is now furthermore provided, to which nitrogen (stream d) is supplied as stripping gas. There are now carbon dioxide and sulfur components (H ₂ S and COS) from the methanol (which is also performed in the stripping) expelled, the

 Sulfur components mostly in the upper column section again

be washed back. The gas (for the most part C0 ₂ and N ₂ ) is then heated via the heat exchanger 201 and led out of the Rectisol scrubber. Cooling performance is required in the Rectisol wash unit, particularly the cooling unit 204, when operating the Rectisol wash 200 in a conventional manner, ie, when the ambient temperature nitrogen is supplied. It goes without saying that cooling can also be required at other points in the process sequence or in the system. In the context of the invention, the nitrogen is now already cooled before it is fed as stream d to the stripping column 210. In this way, the additional cooling capacity, for example in the cooling unit 204, can be reduced.

In FIG. 3, both the air separation plant 100 and the stripping unit 210 of the rectisol scrubbing are shown for this purpose. The nitrogen provided by the air separation plant 100 (stream b) is first supplied to the expansion turbine 300.

The expansion turbine 300, the nitrogen is now relaxed and cooled at the same time. In this case, the expansion turbine or its operation can be configured such that a desired pressure reduction and at the same time a desired cooling is achieved. The energy extracted from the nitrogen by the relaxation and cooling can now be recovered, for example, via a generator as electrical energy (or generally as work). This energy can then be used, for example, for operating pumps or other equipment in the Rectisol wash unit. After leaving the Expansionsturinbe 300, the - now relaxed and cooled - nitrogen (stream d) of the stripping 210 can be supplied. Due to the already pre-cooled nitrogen, a significantly lower cooling capacity is now required in the Rectisol wash unit.

In Figure 4, the structure of Figure 3 is shown again, but here is now a compressor 310 is provided, with which the stream b is compressed prior to expansion, in order to achieve a total cooling to lower temperatures. The compressor 310 may be designed as a turbine booster and directly from the turbine 300th

are driven.

Claims

claims 1 . 1 . Method for purifying a gas (e), in which unwanted components are washed out of the gas (e) in a gas scrubbing unit (200) by means of a scrubbing medium (h),  wherein the undesired components are expelled from the washing medium (h) at least partially using nitrogen (b) as the stripping gas in a stripping unit,  characterized in that the nitrogen (b, f) is cooled before being supplied to the stripping unit (210). 2. The method of claim 1, wherein the nitrogen (g, f) by means of a  Expansion turbine (300) is cooled and at the same time relaxed  3. The method of claim 2, wherein recovered by the expansion turbine (300) from the nitrogen (b) energy is fed back into an energy system and / or used to drive at least one device. 4. The method of claim 2 or 3, wherein additional nitrogen, which should not be supplied to the gas scrubbing unit (200), also by means of  Expansion turbine (300) is cooled and at the same time relaxed. 5. The method according to any one of claims 2 to 4, wherein the nitrogen (b) to a pressure between 2.1 bar and 2.6 bar, or, if a use of the nitrogen (b) is provided for an adsorption, between 2, 6 bar and 3.6 bar is relaxed. 6. The method according to any one of claims 2 to 5, wherein a pressure of the nitrogen (b, f) is increased by means of a compressor before it is cooled. 7. The method according to any one of the preceding claims, wherein the nitrogen (b, f) is cooled by means of a heat exchanger. 8. The method according to any one of the preceding claims, wherein the nitrogen (b, f) is cooled to 0 to -100 ° C. A process according to any preceding claim, wherein the nitrogen (b) supplied to the gas scrubber unit (200) is in one  Air separation plant (100) is obtained. Plant for purifying a gas with a gas scrubbing unit (200), which is adapted to wash out unwanted components from the gas (e) by means of a scrubbing medium (h), and  at least partially expelling the unwanted components from the wash medium (h) using nitrogen (b) as the stripping gas in a stripping unit (210),  characterized by a cooling device (300), which is arranged such that the nitrogen (b) passes through the cooling device (300) before it  Stripping unit (210) is supplied. Plant according to claim 10, wherein the cooling device comprises an expansion turbine (300) and / or a heat exchanger. 12. Plant according to claim 10 or 1 1, further comprising an air separation plant (100) for providing nitrogen (b), which is arranged such that the nitrogen (b) of the cooling device (300) is supplied.