DE3020656A1 - Adsorptive sepn. of combustible materials from gas mixt. - by multiple active carbon stages with interstage cooling of gas - Google Patents

Abstract

The adsorptive sepn. by active carbon of combustible hydrocarbons and/or solvents from gas mixts. with low (up to 12 vol.%) oxygen content in a multi-stage process involves cooling the mixt. after each succeeding stage to approx. its temp. on entering that stage. The material absorbed at each stage is recovered by known desorption methods, e.g. with steam. Also claimed is the appts., a vertical or horizontal column divided into separate chambers each contg. a body of activated carbon with a free space before and after. From the space following each body of carbon the gas passes to an external cooler and is then returned to the space before the next body of active carbon. Used e.g. for recovering hydrocarbons from the gas emerging on filling fuel tanks, after addn. of inert gas (nitrogen, methane) to reduce explosion risk. Since large volumes of air are not added (as with known systems) the appts. is compact, and the final emission is low in pollution.

Description

Process and apparatus for adsorptive separation

of hydrocarbons and / or solvents from gas mixtures The invention relates to a method for the adsorptive separation of combustible Hydrocarbons and / or solvents of high concentration from oxygen-depleted Gas mixtures of activated carbon and also includes an adsorption apparatus for implementation of the procedure.

Containing hydrocarbons and / or solvents in high concentration Gas mixtures whose treatment requires special measures due to the risk of explosion often occur in considerable quantities. For example, when filling of fuel tanks the gas fillings contained in them as so-called breathing gas repressed. If this breathing gas is allowed to flow out freely, which is because of the risk of explosion mentioned is problematic in itself, it not only leads to considerable environmental pollution, but at the same time it also leads to high losses of valuable materials. These breathing gases can depending on the ambient temperature and the properties of the mineral oil products that these Have released gas mixtures, concentrations of hydrocarbon compounds contain up to approx. 1000 g / m3.

The prior art stands for the treatment of non-oxygen-depleted Various methods are available for gas mixtures. The familiar treatment by adsorption by means of activated carbon in the various adsorption devices with a monobed, such as vertical, Horizontal and ring adsorbers, sets the lowering of the Hydrocarbon concentration below the lower explosion limit by dilution the exhaust with air ahead. On the one hand, this is necessary in order to Adsorption occurring temperature increase to keep within the limits that are sufficient Separation of the hydrocarbons allows, and on the other hand, to compliance to ensure the safety regulations. Significant disadvantages of this procedure result from the necessary 20 to 40-fold dilution of the exhaust gas Air, which inevitably results in high system and energy costs.

Furthermore, there are methods and apparatus for the combustion of these gas mixtures known. Here, however, the valuable substances contained in them are destroyed, with in many cases there is no possibility of using the heat of combustion is. Finally, the gas mixtures can also have a low-temperature condensation subsequent incineration or adsorption. Even with this combined The procedure results in safety problems and a high outlay on equipment and energy.

The invention is based on the object of a method of the above to provide designated genus, which the adsorptive treatment of not gas mixtures diluted with air and the recovery of the valuable substances contained therein, without temperature increases during the adsorption process that would impair the separation, made possible in an economical way. This is based on gas mixtures, those to lower the oxygen content or for the transfer in the ignition-safe area not participating in the adsorption process, e.g. an inert gas such as nitrogen or methane (natural gas) has been added.

The problem posed is achieved according to the invention in that the Gas mixtures subjected to a multi-stage adsorption and between the individual Adsorption steps are cooled, whereupon the adsorbed by the activated carbon Hydrocarbons and / or solvents in a manner known per se by desorption be recovered.

The method according to the invention allows a controlled course of adsorption at temperatures favorable for the separation of the hydrocarbons. The ones in the heat of adsorption absorbed by the non-adsorbed Gaq is between the stages are discharged in a controlled manner by means of suitable gas coolers. Because the gas mixtures are not diluted with air, are proportionate with the method according to the invention to treat small amounts of gas, which enables economical apparatus dimensions . The desorption of the activated carbon loaded with hydrocarbons can be carried out in a known manner Way to be done with steam. The exhaust gas produced after adsorption, from which practically all hydrocarbons with 5 or more carbon atoms have been removed thermal afterburning with integrated heat recovery are fed.

This avoids hydrocarbon emissions and reduces energy losses, depending on the efficiency of the combustion and the heat recovery in economic Limits kept.

In order to rule out the risk of explosion, one leads to the invention process of adsorption gas mixtures with a maximum oxygen content of about 12% by volume.

The process is advantageously carried out so that one in the individual Adsorption stages a pre-separation of the various hydrocarbons receives. In accordance with this selective pre-separation, the individual activated charcoal beds are also made of the various stages of adsorption is also selectively desorbed. This is achieved In the case of multi-component gas mixtures, a pre-separation of the gas mixture is used, which is more selective Effect becomes more favorable with the myriad of adsorption stages used.

The intercooling is so in the pursuit of the inventive idea made that the gas mixtures after each adsorption about their to the the input temperature belonging to the relevant stage.

For a controlled adsorption process and also for the limitation the heat of adsorption occurring per stage, it is important that the bulk heights of the individual activated carbon beds of the successive adsorption stages depending on the heat of adsorption occurring and the width of the mass transition zone of the individual hydrocarbons can be selected.

During the desorption step, the desorption gases from the individual Activated charcoal beds in succession to one or more condensation devices at the same time are fed to the pre-separation of the hydrocarbons.

A particularly suitable one for carrying out the method according to the invention Adsorption apparatus with a gas enters at one end and one Gas outlet at the other end is characterized in that it is in a standing container a plurality of one above the other, which are closed off from one another by dividing floors Rehandlungsa men is provided, in each of which one the Be-10c'11 terquerscbni tt filling, gas-permeable support floor for the AL-tivizohlfill underneath Formation of an entrance area under the shelf and an exit area above the activated charcoal bed is arranged, wherein the exit space and the entrance space Adjacent treatment rooms each with the interposition of a cooler are connected.

An alternative embodiment that can be chosen when the space required for an upright container arrangement is not given, is characterized in that a A plurality of arranged side by side and separated from each other by separating lands Treatment rooms are provided, in each of which two the container cross-section filling, gas-permeable retaining walls at a distance of the respective intended layer thickness of activated carbon with the formation of an entrance space on one side of the activated carbon layer and an exit space on the other side of the activated carbon layer, the The exit room and the entrance room of adjacent treatment rooms are each interposed of a cooler are connected to each other.

Both embodiments of the adsorption apparatus according to the invention What is common is that all adsorption stages are arranged within a single container are, whereby the adsorber has small dimensions and a correspondingly small one Requires installation space. A plant system can consist of one or more adsorbers exist.

If several adsorbers are used, these can be operated non-switchable so that adsorption and absorption are simultaneously in different Apparatus are carried out, which enables a quasi-ion-continuous operation will.

To the adsorption apparatus according to the invention for carrying out the To form desorption> the arrangement is expediently made in such a way that the exit belts each of the treatment rooms is provided with a supply line for the desorbent are and that to the entrance rooms of all treatment rooms 2 # leads for the respective Desorbate are connected.

The method according to the invention and that provided for its implementation Adsorption apparatus are not only useful for the treatment of respiratory genes Afineral oil tanks, it can of course also contain low-oxygen gases with high Treated hydrocarbon and / or solvent fractions of different origins verden, as they occur e.g. on machines that are used to dry products Gas mixtures are circulated.

The adsorption apparatus according to the invention is described below with reference to FIG Schematic drawings depicting various exemplary embodiments in greater detail explained. 1 shows an upright adsorption apparatus and 2 shows an adsorption apparatus arranged horizontally.

The adsorption apparatus shown in Fig. 1 has an elongated one cylindrical container 1, the top and bottom each by a bottom 2 or 3 closed is. Inside the container 1 provided Separating floors 4 to 7 divide the rehabilitation container 1 into five separate ones one above the other arranged treatment rooms 8 to 12, which have a matching Can have volume. The number of treatment rooms depends on the Number of intended adsorption stages.

The container cross-section is located in the treatment rooms 8 to 12 filling, gas-permeable support floors 13 to 17, each of which has a support base is provided in every treatment room.

Activated charcoal beds 18 to rest on the support floors 13 to 17 22, whose Elöhe is adapted to the desired course of adsorption. Every treatment room has an entrance room below the top and above the hktivohl # scüLUNG an exit space for the gas mixture to be treated. In Fig. 1, reference numerals denote 23 to 27 the entrance rooms and 28 to 32 the exit rooms To the entrance room 23 of the treatment room 8, the gas inlet 33 is connected, while the gas outlet 34 adjoins the output space 32 of the treatment space 12, so that the adsorption apparatus to be treated gas mixture through the container 1 through an upwardly directed Takes away. This flows through the gas inlet 33 into the inlet space 23 the gas mixture entering the treatment room 8 reaches the activated charcoal bed 18 into the outlet space 28, where it is via a connecting pipe 35 after flowing through a external cooler 36 in the entrance room 24 of the next treatment room 9 entry. The following treatment rooms are in a corresponding manner 37 to 39 connected to one another with the interposition of a cooler. After graduation of the adsorption process, i.e. after all charcoal dumps have flowed through 18 to 22, the treated gas mixture leaves the exit space 32 of the upper treatment space 12 via the gas outlet 34, which is connected to an afterburning system (not shown) can be connected.

The external coolers 36 to 39 can be of the fin type. Instead of external coolers, coolers arranged inside in container 1 can also be used be provided. The cooling medium used is water that flows in and out via line 40 return via line 41. In the intercoolers 36 to 39 each is the Adsorption heat from the previous stage absorbed by the gas mixture is removed, i.e. transferred to the cooling medium.

When the adsorptive capacity of the activated carbon beds is exhausted is, the gas inlet 33 is shut off and the line 42 is used as a desorbent used steam introduced. This enters all exit rooms 28 to 32 and develops its desorbing effect in the activated charcoal beds 18 to 22.

The desorbate reaching the entrance rooms 23 to 27 is either Discharged via the collecting line 43 or stepwise via the dashed lines Lines 44 to 48 for pre-separation of the hydrocarbons adsorbed in the individual stages deducted.

The desorbate is in a known manner in downstream capacitors liquefied, then cooled and finally fed to a separation.

Instead of the upright container arrangement described with reference to FIG A horizontal arrangement can also occur, as shown in FIG. 2. the The horizontal arrangement basically has the same structure as the vertical arrangement, which is made clear by using corresponding reference numbers in FIG will.

The lying elongated container l is at both ends closed by end walls 2 'and 3' and is also in this case to achieve a five-stage absorber through partition walls 4 to 7 into five equally sized treatment rooms 8 to 12 divided.

In the treatment rooms 8 to 12 there are again layers of activated carbon 18 to 22 entrance rooms 23 to 27 and exit rooms 28 to 32.

The activated carbon layers 18 to 22 are each gas-permeable between two Retaining walls 49 and 50 fixed in their position. The distance between the retaining walls 49> 50 corresponds to the thickness of the activated carbon layer desired for the respective adsorption stage. Located between the exit room and the entrance room of adjacent treatment rooms in turn interposed external coolers 36 to 39, which are based on the The type described with reference to FIG. 1 can be operated. The same applies to the Lines that carry the desorbent and the desorbate, or the desorbates.

The method according to the invention is illustrated below with the aid of two examples, of which example 1 is a comparative example, explained in more detail.

Example 1 At a loading station for petroleum products, as Breathing gas when filling tanks a gas volume of 1000 m3 / h at an average temperature from 200C on.

The gas mixture had that given in Table 1 below average composition.

Table 1 Component Volume fraction Concentration Vol .-% g / m3 C2 0.86 10.75 C3 0.66 12.09 C4 14.45 349.11 Cg 3.81 114.26 C6 0.83 29.71 C7 c7 Benzene 0.29 approx. 11.02 + Toluene Air + toluene 79.10 The total of hydrocarbons (KW) was therefore an average of 526.94 g / m3. The lower explosion limit (LEL) of the gas mixture was between about 37 and 40 g / m3.

The gas mixture was made in accordance with the explosion protection guidelines of the employers' liability insurance association to a HC concentration below the lower explosion limit diluted with air. To maintain a prescribed safety distance to the LEL a dilution to 50% of the LEL would have been used. This would have been a concentration of 18g KW / m³ or a dilution of about 30: 1. Because of occurred HC concentration peaks of up to about 900 g HC / m3 in the breathing gas were determined according to the previous applications a dilution up to about 50: 1 used, which is a concentration of about 10.5 g KW / m3. The total volume flow was 50,000 m3 / h.

This gas mixture continuously became one of three connected in parallel Adsorbers with an existing adsorption system with activated carbon 4tono bed, each of which two adsorbers were kept in adsorption mode while the third was in desorption mode. The form of the adsorbers was lying down Cylinders with a diameter of 2.6 m and a length of 8.0 m.

Each adsorber had a lower gas distribution space with a gas supply and a distributor base arranged above it, which doubles as a support grate served for the activated carbon. Above the activated carbon there was a collecting space with gas discharge arranged. The total activated carbon filling of the adsorption system was about 30 t. The desorption took place with saturated steam at 1200 c and 3 bar pressure, with an amount of steam of 1,5oo kg / h. The electrical energy required to deliver the gas mixture was about 170 kW / h. There were 100 m3 / h of cooling water at 25 0C for condensation and cooling the desorption steam is used up.

The investment costs of the adsorption-desorption system described amounted to about 1.2 million DM.

The exhaust gas leaving the adsorption system still contained essentially the amounts of C2 and C3 that have not been separated out and about 60% of the existing Cq These C4 emissions represent a significant environmental impact. Contained in total the exhaust gas still has about 4.5 to 5 g / m3 of C2 to C4 in order to achieve an afterburning at about To enable 800 ° C, the exhaust gas would have an uneconomically large amount of support gas (Natural gas) must be added.

Example 2 The breathing gas flow according to Example 1 of 1000m³ / h were for oxygen depletion in order to achieve an extra- half the Gas mixture 430 m3 / h methane (natural gas) is added to the explosive limits. The resulting total volume flow of 1,430 m3 / h had the composition according to table 2.

Table 2 Component Volume fraction Concentration Vol.% G / m3 C1 30.0 c2 0.60 7.5 C3 0.46 8.42 C4 10.10 244.42 C5 2.66 79.80 C6 0.58 20.76 > c7 Benzene 4 0.20 7.60 + Toluene Air 55.40 The total of hydrocarbons (excluding methane) therefore averaged 368.50 g / m3. This gas mixture was continuously fed to an adsorption system operating according to the method according to the invention, which essentially consisted of two multi-stage adsorbers of the type shown in FIG. The diameter of the upright adsorber was 1.6 m and its height was 7.5 m.

Each of the adsorbers, which take turns in the adsorption / De.

Sorptionsbetrieb were driven, had five levels with from below upward rising activated carbon dumping height. The total amount of activated carbon in the adsorption system was 3 t with a grain size of 3 to 4 mm (as in Example 13. The activated charcoal beds rested on shelves with a width of about 2 mm.

The activated carbon filling was on the five levels approximately according to the table 3 distributed.

Table 3 Level 1 2 3 4 5 Proportion by weight 8 13 21 26 32 This distribution allowed both a controlled course of adsorption and the effective limitation of the heat of adsorption occurring in the individual stages, since the widths of the mass transition zones for the HC main components C4 and C5 are greater than the activated charcoal bed heights in the lower stages. The adsorption heat absorbed by the non-adsorbed gas in the individual stages was dissipated between the stages through lamellar coolers using water at 25 ° C as the coolant.

Depending on the migration speed of the main adsorption zone and the intermediate cooling, the maximum temperature profile given in Table 4 was reached in the adsorbers during the migration. Table 4 Level 1 2 3 4 5 inbound temperature 30 35 35 32 30 oc Starting temperature 79 79 75 65 60 oc This procedure according to the invention not only enables the desired separation of HCs (higher than C5), but there is also a certain degree of selective separation of the HCs supplied in the individual stages. The composition of the K deposited at the end of the loading is shown in Table 5.

Table 5 Level separated KW composition replacement Wt% ~ C5H12 + C4H10 2 2 C6H14 42.7 C4H10 4.7 C6H1 4 0.4 3 C5H12 90.3 C4H10 9.3 C5H12 78 4 C4H10 2 5 C5H12 C4H10 39 The hydrocarbon-depleted gas mixture (separated C5 and higher) emerging from the stage adsorber during the adsorption could be fed directly to a thermal post-combustion with an integrated heat recovery system, because its C2 to C4 content of about 230 to 240 g / m³ and its content of about 31 Vol.% Methane was combustible without supporting gas. The exhaust gas volume flow was only about 1410 m3 / h. The afterburning prevented hydrocarbon emissions and the energy losses were kept within economically justifiable limits, depending on the efficiency of the afterburning and the energy recovery.

The desorption of the HC from the loaded activated carbon also took place in In this case, steam at 1200C and 3 bar pressure, with desorption only about 800 kg / h were consumed. The desorption could be used for all desorption stages be carried out together, if no pre-separation of the Kld was desired, they but could also be carried out selectively from the individual stages with pre-separation of the KW will. The condensation of the desorption steam and the cooling of the desorbate condensate took place with water-cooled heat exchangers. About 50 m3 / h of cooling water were used for this needed. For intermediate cooling of the gas mixture after adsorption stage 1 Up to 4 about 14 m3 / h of cooling water at 25 0C were used.

After the desorption, the adsorber was circulated with Gas cooled down to the necessary temperature and stood for reloading the activated carbon is available. For the conveyance of the breathing gas through the Adsorber no additional energy was required, as the pressure required to deplete the oxygen gas used for this purpose was exploited. The investment costs for the described Adsorption / desorption plant amounted to about 0.7 million DM.

The comparative for the assessment of Examples 1 and 2 Significant numerical values are given below compiled in table 6.

Table 6 Example 1 Example 2 Total gas volume flow at the absorber inlet 50 000 1 430 m3 / h HC concentration at the absorber inlet 10.5 368.5 g / m3 (without methane) Activated charcoal filling quantity 30 3 t Energy consumption for Gas mixture delivery 170 0 kw / h Water vapor consumption for desorption 1 600 800 Cooling water consumption m3 / h loo 64 Investment costs 1.2 0.7 Million DM

Claims (9)

Claims Process for the adsorptive separation of flammable hydrocarbons and / or solvents of high concentration from oxygen-depleted gas mixtures of activated carbon, characterized in that the gas mixtures undergo a multi-stage adsorption subjected and cooled between the individual adsorption steps, whereupon the hydrocarbons and / or solvents adsorbed by the activated carbon in be recovered in a known manner by desorption. 2. The method according to claim 1, characterized in that one of the Adsorption gas mixtures with a maximum oxygen content of about 12 vol. 3. The method according to claims 1 and 2, characterized in that that one pre-separation of the various hydrocarbons in the individual adsorption stages brings about. 4. Process according to Claims 1 to 3, characterized in that the gas mixtures after each adsorption stage approximately to their level for the relevant stage corresponding inlet temperature can be cooled. 5. Process according to claims 1 to 4, characterized in that that the bed heights of the individual activated carbon beds of the successive Adsorption stages according to the heat of adsorption occurring and the width of the mass transition zone of the individual hydrocarbons can be selected. 6. The method according to claims 1 to 5, characterized in that that the desorption gases from the individual activated carbon beds one after the other or at the same time several condensate devices for the pre-separation of the hydrocarbons are fed. 7. Adsorption apparatus for carrying out the method according to the claims 1 to 6, with a gas inlet at one end and a gas outlet at the other end, characterized in that in a standing container (1) a plurality of through Separating floors (4-7) treatment rooms which are closed off from one another and arranged one above the other (8-12) is provided, in each of which a gas-permeable filling the container cross-section Support floor (13-17) for the activated charcoal bed (18-22) to form an entrance space (23-27) under the shelf and an exit space (28-32) above the activated charcoal bed is arranged, the exit room and the entrance room of adjacent treatment rooms are connected to each other with the interposition of a cooler (36-39) (Fig. 1). 8. Adsorption apparatus for carrying out the method according to the claims 1 to 6, with a gas inlet at one end and a gas outlet at the other end, characterized in that in a lying container (1 ') a plurality of Treatment rooms arranged next to one another and closed off from one another by partition walls (4-7) (8-12) is provided, in each of which two gas-permeable Retaining walls (49, 50) at a distance of the respective intended layer thickness of activated carbon forming an entrance space (23-27) on one side of the activated carbon layer (18-22) and an exit space (28-35) on the other side of the activated carbon layer, the exit room and the entrance room of adjacent treatment rooms, respectively are interconnected with the interposition of a cooler (36-39) (Fig. 2). 9. Adsorption apparatus according to claim 7 or 8, characterized in that that the exit rooms (28-32) of the treatment rooms (8-12) each with a supply line are provided for the desorbent and that to the entrance rooms (23-27) of all Treatment rooms discharges for the respective desorbate are connected.