DE102020001331B4 - Method for separating paraffins from a gas stream - Google Patents

Abstract

Method for separating paraffins from a gas stream, wherein a gas stream containing paraffinic hydrocarbons is fed to a separation tower (2) in which it is mixed with a stream of a cooling medium, wherein the mixture of gas stream and cooling medium is cooled to a temperature below the freezing temperature of the paraffinic hydrocarbons, whereupon the paraffinic hydrocarbons condense and/or freeze out and are deposited at the bottom of the separation tower (2).
characterized by
that the mixture of gas stream and cooling medium is partially recirculated by drawing off part of the mixture from a lower section of the separation tower (2) and feeding it back into the headspace (3) of the separation tower (2) and
Liquefied or cold gaseous nitrogen is used as the cooling medium.

Description

The invention relates to a method for separating paraffins from a gas stream.

Particularly in the production of adhesives, sealants, rubbers, paints and varnishes, as well as for products in the cosmetics, pharmaceutical, paper, and food industries, exhaust gas streams are generated that are laden with paraffinic hydrocarbons (hereinafter referred to as saturated chain hydrocarbons with the general formula _{CnH2n +2} ). These paraffinic hydrocarbons pose a particular problem because they are difficult to remove from the gas stream and tend to form deposits on the equipment used to clean the gas stream, necessitating regular maintenance and cleaning of the equipment.

From the EP 1286 160 A1 A test device for examining the exhaust gases of injection engines, particularly diesel engines, is known. The test device includes a pre-assembly unit with a ceramic filter arrangement for separating, among other things, unburned paraffin oils. However, this arrangement is not suitable for large-scale treatment of exhaust gas streams.

From the US 32 283 026 A A process is known in which a raw gas loaded with paraffins is treated with a paraffin-containing washing medium, whereby the paraffins are washed out of the raw gas.

From the US 3 362 989 A A method for producing terephthalic acid by sublimation from a gas stream is known. However, the findings obtained there cannot be readily transferred to the treatment of paraffin-containing gas streams.

The DE 10 2007 034 787 A1 This describes a device in which a product, particularly a free-flowing or liquid product, is treated in a reactor with a gas stream, whereby substances contained in the product, such as water, are carried along by the gas stream. To reduce gas consumption, the gas is at least partially recirculated.

Attempts have also been made to remove the paraffinic hydrocarbons from the gas stream in a separate process step. This has mostly been done using activated carbon filters. However, activated carbon filters have the disadvantages of a comparatively short lifespan, poor regenerability, and the problem of the resulting paraffin-carbon mixture being highly flammable.

The invention is therefore based on the objective of providing a method for removing paraffinic hydrocarbons from a gas stream, in particular an exhaust gas stream, which overcomes the disadvantages of the prior art.

This problem is solved by a method with the features of claim 1.

In the inventive process for separating paraffins from a gas stream, a gas stream containing paraffinic hydrocarbons is fed to a separation tower in which the gas stream is mixed with a stream of a cooling medium, wherein the mixture of gas stream and cooling medium is cooled to a temperature below the freezing temperature, but at least below the condensation temperature of the paraffinic hydrocarbons contained in the gas stream, whereupon the paraffinic hydrocarbons condense and/or freeze out and are separated at the bottom of the separation tower.

According to the invention, the gas stream to be treated is directly cooled by the cooling medium to a temperature below the condensation temperature, preferably the freezing temperature, of the paraffinic hydrocarbons contained in the gas stream. If several different paraffinic hydrocarbons are present in the gas stream to be treated, the temperature to which the mixture of gas stream to be treated and cooling medium is cooled in the separator tower should preferably be below the lowest condensation temperature, and particularly preferably below the lowest freezing temperature, of the paraffinic hydrocarbons contained in the gas stream. For example, the mixture in the separator tower is cooled to below 40°C, preferably below 20°C. The paraffinic hydrocarbons contained in the gas stream condense and/or freeze out and collect, at least to a large extent, at the bottom of the separator tower. In this way, the gas stream to be treated is at least largely freed from paraffinic hydrocarbons. The condensed or frozen paraffins are removed from the separation tower and can be used for other purposes. The removal of the paraffins from the separation tower is carried out either during the treatment of the gas stream by continuous or intermittent extraction using a sluice gate, or in batches following the treatment of each gas stream. The process according to the invention is particularly effective without absorption ionizing agents or filter equipment and related, elaborate regeneration or cleaning systems.

To use the cooling medium as efficiently as possible, the mixture of gas stream to be treated and cooling medium is partially recirculated. It is drawn from a lower section of the separation tower by means of a blower and fed back into the separation tower via a head chamber.

The cooling medium used in the process according to the invention should be inert with respect to the gas stream to be cleaned. A preferred cooling medium is liquefied or cold gaseous nitrogen.

A device suitable for carrying out the process according to the invention comprises a separator tower into which an inlet for a gas stream to be cleaned, an outlet for cleaned gas, a separator line leading from the bottom of the separator tower for removing condensed and/or frozen paraffinic hydrocarbons, and an inlet for a cooling medium open. Preferably, the inlet for the gas stream to be treated, as well as the inlet for the cooling medium, opens into an upper section (headspace) of the separator tower. The outlet for the cleaned gas stream exits the separator tower below these inlets, but above the separator line for the paraffin, which preferably exits at the lowest point of the separator tower.

A particularly advantageous design of the device allows for partial recirculation of the mixture of gas stream to be treated and cooling medium, thus ensuring efficient utilization of the cooling medium's cooling capacity. For this purpose, a recirculation line equipped with a fan leads from a lower section of the separator tower to the top chamber of the separator tower, where it connects either directly to the separator tower, to the supply line for the gas stream to be treated, or to the supply line for the cooling medium.

Preferably, the separation line for the condensed and/or frozen paraffin is equipped with a rotary valve, in particular a rotary valve. This allows the condensed or frozen paraffin to be continuously drawn off from the separation tower while the device is in operation, i.e., while a gas stream to be treated is being cooled in the separation tower.

The process according to the invention is suitable for treating exhaust gas streams loaded with paraffinic hydrocarbons, which can otherwise lead to undesirable deposits on filters, in pipelines, valves, or other components. In particular, the invention is suitable for cleaning exhaust gas streams in the production of adhesives, sealants, rubbers, paints and varnishes, as well as for products in the cosmetics, pharmaceutical, paper, and food industries. The separated paraffin is collected and can be used for further purposes; however, the production of paraffins is not part of the present invention.

An embodiment of the invention will be explained in more detail with reference to the drawing. The only drawing ( 1 ) schematically shows the circuit diagram of a device for carrying out the method according to the invention.

The in 1 The device 1 shown comprises a separator tower 2, into the head chamber 3 of which a supply line 4 for a gas stream loaded with paraffinic hydrocarbons, in particular an exhaust gas stream, opens. A supply line 5 for a cooling medium also opens into the head chamber 3 of the separator tower 2, the flow of which can be regulated by means of a valve 6. An outlet 7 for purified gas (clean gas) opens from a central region of the separator tower 2. At approximately the same level as the outlet 7, a return line 8 leads from the separator tower 2. A blower 9 is arranged in the return line 8. In the embodiment shown here, the return line 8 opens downstream of the blower 9 into the supply line 5 for the cooling medium; however, within the scope of the invention, it is equally conceivable that the return line 8 opens directly into the head chamber 3 or into the supply line 4. At the lowest geodetic point of the downwardly tapering funnel-shaped separation tower 2, a separation line 10 for the removal of frozen or condensed paraffin opens, in which a sluice 11, for example a rotary valve, is arranged.

During operation of the device 1, a gas stream laden with one or more different paraffinic hydrocarbons, for example, an exhaust gas stream from a manufacturing process for adhesives or sealants, is fed into the separation tower 2 via the supply line 4. Simultaneously, a cooling medium, for example, liquid or cold gaseous nitrogen, is supplied via the supply line 5. The cooling medium mixes with the supplied gas stream inside the separation tower 2 and cools it. In doing so, the cooling medium absorbs heat from the gas stream and may evaporate.

By continuously supplying cooling medium via the supply line 5, the gas mixture forming inside the separator tower 2 is cooled to a temperature below the condensation temperature of the paraffins in the gas stream, for example, to a temperature below 40°C. Preferably, the cooling is carried out to a temperature below the solidification temperature of the paraffin with the lowest solidification temperature contained in the gas stream. The temperature can be controlled to a predetermined value by, for example, regulating the flow rate of the cooling medium supplied via the supply line 5 at the valve 6 as a function of a measured parameter, such as a temperature inside the separator tower 2 detected by a sensor 12 or (not shown here) a concentration of paraffins in the clean gas measured at the outlet 7, which should not exceed a predetermined maximum concentration.

To make the best possible use of the cooling medium's cooling capacity, a partial flow of the gas mixture located in the lower section of the separator tower 2 is drawn off via the return line 8 by means of the blower 9 and reintroduced into the head chamber 3 of the separator tower 2. Since the temperature of the gas mixture returned via the return line 8 is lower than the temperature of the gas flow supplied via the supply line 4, it contributes to the cooling in the head chamber 3 and thus supports the cooling medium supplied directly via the supply line 5. The purified gas flow is discharged via the outlet 7.

As the gas mixture cools, the paraffins in the gas stream condense or freeze and collect at the bottom of the separator tower 2. From there, they are discharged via the separator line 10 and disposed of or used for further processing. The airlock 11 allows for the continuous transport of paraffins out of the separator tower 2 even during gas purification, ensuring that no, or only a negligible, portion of the gas mixture escapes from the separator tower 2 via discharge.

Furthermore, the device 1 can be operated continuously, in which a loaded gas stream is constantly supplied via inlet 4 and purified gas is discharged via outlet 7, as well as in batch operation, in which a predetermined quantity of gas is supplied to the separator tower 2, which is then treated with cooling medium from inlet 5 until a predetermined degree of gas purification is achieved. For the latter case, inlet 4 and outlet 6 can each be equipped with a valve 13, 14.

Reference symbol list:

1

device

2

Separation tower

3

headspace

4

supply line

5

supply line

6

valve

7

Detoxification

8

Return line

9

fan

10

Separator line

11

sluice

12

Temperature sensor

13

valve

14

valve

Claims (1)

A method for separating paraffins from a gas stream, wherein a gas stream containing paraffinic hydrocarbons is fed to a separation tower (2) in which it is mixed with a stream of a cooling medium, wherein the mixture of gas stream and cooling medium is cooled to a temperature below the freezing temperature of the paraffinic hydrocarbons, whereupon the paraffinic hydrocarbons condense and/or freeze out and are separated at the bottom of the separation tower (2), characterized in that the mixture of gas stream and cooling medium is partially recirculated by drawing off a portion of the mixture from a lower section of the separation tower (2) and feeding it back into the top space (3) of the separation tower (2), and liquefied or cold gaseous nitrogen is used as the cooling medium.