WO1993002771A1

WO1993002771A1 - A method and an apparatus for cleaning extensive air volumes containing low concentrations of pollutants of hydrocarbons

Info

Publication number: WO1993002771A1
Application number: PCT/SE1991/000510
Authority: WO
Inventors: Lennart Stolpe
Original assignee: Rådia Kb
Priority date: 1990-02-02
Filing date: 1991-08-01
Publication date: 1993-02-18
Also published as: SE9000386D0; SE467238B; SE9000386L; EP0556192A1

Abstract

The present invention relates to a method and an apparatus for cleaning extensive air volumes containing low concentrations of pollutants of hydrocarbons, with which method and apparatus the hydrocarbons are caught during a first phase in an active carbon or a metal filter alternatively a honeycombed vessel surface covered by active carbon or any other adsorbent, whereafter during the consecutive phase the caught hydrocarbons are released and converted in a conventional catalyst (11) to carbondioxid and water. The apparatus comprised of one filter (1) mounted in a ventilation system for the process air, which by use of a trottle (8) can be sealed off from the process air and thereby create mainly a closed circuit, where the filter (1) is converted to a mixing chamber (16) connected to a heating battery (10) which in turn is connected to a catalyst (11) for further transport of the cleaned air mixture via an inlet (17) containing a fan (12) and a heating battery (13) and back to the filterbeds existing in mixing chamber (16) in order to recondition the same.

Description

A method and an apparatus for cleaning extensive air volumes containing low concentrations of pollutants of hydrocarbons.

Existing cleaning techniques tailored for the exhausted of environmentally hazardous substances like solvents and styrenes, considering today's emission limits, are extremely expensive and show a maintenance level which widely exceeds the financial capacity of small and middle- sized companies. The reason to this is mainly the low concentration of pollutant considering the large air exchange volumes and thereby the need of expensive concentration equipment prior to final treatment either by catalytic or thermal combustion alternatively recycling. Existing cleaning techniques also requires large amounts of energy in cleaning of the polluted air and consequently high costs. As a normal practice this polluted air has been passed on freely into the atmosphere without any prior treatment.

The object of the present invention is to provide a method and apparatus as initially described which eliminates mentioned drawbacks. The essentially distingvishing features of the invention are stated in the claims enclosed.

As a result of the present invention there are now possible to achieve a level of cleaning of as high as 85 %. Furthermore the invention will give a highly efficient catalytic combustion, low energy consumption, low maintenance costs due to use of exchangeable cassettes for the regenerable filterbeds, fully automised and computerised control with datalogging, automatic alarm functions for temperatures and exceeded emissi on l evel s and prewarning of upcoming exchange of filterbeds.

The invention will now be described in more detail below with reference to enclosed drawings which

Fig. 1 shows a prefered, first embodiment of an apparatus for the carry out the method according to the invention to clean large air volumes with low concentration of hydrocarbons.

Fig. 2 shows a second embodiment of the apparatus shown in

Fig.1

Fig. 3 shows schematically a third embodiment of the apparatus for the cleaning in the form of a complete system and

Fig. 4 shows a schematic sectional view of a filter included in the apparatus shown in Fig. 3.

The embodiments of the apparatus shown in Fig. 1-4 for the carry out of the method according to the present invention intended in the first phase to catch the actual hydrocarbons, for instance solvents, styrene etc.. either in a bed of pretreated active carbon on a metalfabric cloth 3, whereafter in a second phase, in a filter 1 previously caught hydrocarbon is released and converted by the use of a conventional catalyst 2, 2' (precious- or base metal) to carbon dioxid (CO2) and Water (H2O).

In Fig. 1 and 2 the apparatus comprises of either one firmly mounted or rotating filter 1, which can be placed in the polluted airflow 4 and will adsorb the present hydrocarbons. The apparatus will thereafter in it's entirety or parts thereof for heating to a temperature which is undercutting the point of combustion for the carbon or the melting temperature of the metalfilter after a preheating period up to approx. 150 °C.

The heating can alternatively be achieved either indirect by locally placed electric heating elements 5 if impregnated/imibedded catalyst 2 is used (Fig.1) or with inblow of hot air, if connected catalyst 2' is used (Fig. 2). Thereafter is the catalyst 2 or 2' starts a reaction known par sa and converts the caught amount of hydrocarbon to carbondiαxid (CO2) and water (H2O).

Under specific circumstances the metal filter might have to be sprayed with a pretreatment via a nozzle 6 prior to heating and catalysis of the collected gas takes place. The apparatus in it's entirety shall at it's use be placed in the airflow 4 and thereby be exposed to the air polluted by hydrocarbons and be engineered to it's thickness, area and airflow per minute, that ail free hydrocarbons are adsorbed (Fig.1). Initially the method of rotating only one filter is covered, although the same result will be achieved with two or more fixed filters 1, in between which the incoming air is allowed to alter from one to the other. In one case exposed, in the other heated and catalysed (regenerated). Later on the method according to Fig.3-4 is covered, where individual, exchangeable and fixed cassetteformated filterbeds are used.

The filter 1 is slowly rotating in the polluted airflow 4 simultaneously as - within a limited segment of the rotation - the filterbed is heated. Within the segment previously caught hydrocarbons are converted to carbondioxid and water. At the same time a regeneration of another segment of the filterbed taken place and a new exposure will be possible. This sequence will be repeated continuously in parallel with cleaning of the polluted airflow.

In the embodiment shown in Fig. 2, when a separate catalyst 2' is used, the filterbed 1 will be penetrated via a separate air channel 7, within the above mentioned segment by hot air, temperature according to the above stipulations, whereby caught hydrocarbons, which now at right temperature for catalysis is led into the catalyst 2'. In those cases metalfliters are use, also specific solvents can be added in order to secure all hydrocarbons to leave the filterbed. The collected amount of hydrocarbons is therafter transported into the catalyst in order to be transformed into the main components, carbondioxid and water. The catalyst may in all cases be either based on platinum (Pt) or with a combination of palladium CPd) and rhodium (Rh) or consist of basemetals like Al-, Cr-, Ni-and their oxides.

As can be seen from Fig.3 the adsorbtion filter 1 is shown how to be mounted with it's assembling parts in an ordinary vent system. Before and after the filter 1 there, is a chamber 9 including a throttle, by means of which a separate circuit, from the vent system's channel can be created for the regeneration process itself. This circuit comprises besides the filter 1 itself and the chambers 9 of one, in the direction of the air flow, heating battery 10, a catalyst 11, from which partly a cleaned air volume leaving the circuit partly an air volume together with other excess air will be fed via a fan 12 to a heating battery 13, where the air is heated on it's way into the filter 1 via one of the chambers 9. In front of the first filter 9 it is also possible to arrange for a particle filter 14. The prepared, Concentrated filterbed confined in the filter 1 in specific cassette modules 15 which is to be cleared from Fig.4. These modules 15 are arranged easy to be exchanged in one by the filter 1 limited and sealed treatment chamber 16. Furthermore are those individual filterbeds in each cassette module 15 individually sealed off from each other by means of on the drawing not shown, automatically controlled house within the treatment chamber 16. The cassette modules 15 are easily exchangeable, angled and orientated in such a way that a maximum of filter area with a minimal of gasresistance and pressure drop is achieved .

In order to avoid ignition from other parts of the connected industrial activity the cassette modules 15 sealed off in a. fireprotected area and sealed off from connected vent system by flame protectors. The filterbeds consists mainly of highly activated carbon which is so prepared that a maximum capacity of adsorbtion is achieved for individual types of hydrocarbons and other pollutants. The filterbed may consist of active carbon, which is pretreated with solvents of inhibitors, solvents of hydroquinone, tertiary butylcatechcl, or similar solutions which delays or prohibits polymerisation of styrene or it's. compounds and thereby make it possible to catch, store and concentrate with consecutive regeneration.

The apparatus shown in Fig.3 functions in the following way, The filter 1 receives the vented process air during working hours of a day, whereby the pollutants in the filterbeds in filter 1 are concentrated. At this point in time the houses 8 in the chambers 9 are in their open position. At a preset hour the filter 1 is closed by means of the houses 8 are moving towards their closed position and the filter is turned into a treatment chamber as a part in a partly closed circuit. The concentrated filterbeds in filter 1 will be air blown at a temperature of approx. 80 °C and thereby gradually release content. The hereby disposed of gas from filter 1 is further transported to the next treatment chamber 10 for further temperature increase prior to catalysis in the catalyst 11 (approx. 350 °C).

A catalytic combustion takes place and transforms the collected pollutants (hydrocarbons) mainly to carbondioxid and water. Exited and cleaned air volume is low ( <100 m-3/h ) and a temperature between 450 -550 °C. This amount of energy is partly reused in the process. Remaining quantity might be used for excess heating either directly or via a conventional heatexchanger. The cleaning system is modularised in 5 or 10.000 m3/h and may be enlarged by multiples of these two flow levels. By means of this method tne concentrated filterbeds may individually and consecutively be treated for regeneration in a closed section of the treatment chamber 16. Those individual filterbeds will be air blown with preheated gas mixture or air within a temperature range 35 < x < 150 °C and thereby dispose off the concentrated caught hydrocarbons to an other closed section in the treatment chamber 16. Therafter may the exited gases be led further on to a heating battery 10 for heating to 200 - 450°C prior to chemical catalysis ar thermal combustion. After the catalyst 11 the heated and catlysed or combusted gases are led to it's main part to an inlet 17 as a. pretreatment of the air meant for the preheating. The entire described sequence will automatically start it's regenerating process when the filterbeds reached a preset level or point in time of exposure Further more the automatic preheating is linked with the exit temperature of the gas or to a preset level. Those in filter 1, regenerated filterbeds may as so wished be blown individually and regenerated to a preset level or completely, whereafter the next filterbed will be regenerated etc.. The exited regenerated gases' temperature is automatically guiding as well blowing volume of gas/air as treatment temperature in order to maximise the catalyst/combustion temperature. Further more the regenerating process is not started up in the treatment chamber prior to the catalyst/combustion temperature reached it's correct working temperature. The regenerating process will return automatically to it's starting point after completing a full circle and allowing new concentration of incoming polluted volumes on all or preselected number of filterbeds, whereby the treatment chamber 16 again will be opened by means of the houses 8. An upgrading of the filterbeds is made in sequence with the finalised regeneration by the individual or all filterbeds by means of fine spray nozzles and in proportion to degradation of the filterbeds and simultaneous cooling of the same in order always to maintain a maximum of capacity in the filterbeds. Finally the apparatus gives automatically an indication if an average working shift can be procassed due to overloading or missing previous regenerazior or other malfunction.

Claims

1. A method for cleaning extensive air volumes containing low Concentrations of pollutants of hydrocarbons, which during a first phase are caught in an active-coal or a metal filter alternatively a honeycombed vessel surface covered by active-coal or any other adsorbent and said hydrocarbons during at least a consecutive phase are released and converted by a conventional catalyst into carbondioxid and water, whereby the polluted airflow is urged to pass the filter (1) during said first phase in a predetermined period of time when said filter is mounted in line in a ventilation system for process air, that after said predetermined period of time the filter (1) is chut off from the process air by aid of closable throttles (8) provided in chambers (9) upstreams and downstreams said filter, whereby said filter

(1) starts to function as treatment chamber (16) in a partly closed circuit and concentrated filter masses in the filter are gas treated during a high temperature to gradually deliver its contents, that said contents are led via the chamber (9) to a heating battery (10) for heating up to about 350°C before catalysation in a subsequent catalyst

(11), in which a catalytic burning takes place and the pollutants existing in the gas are converted mainly to carbondioxid and water, that the obtained, cleaned gas mixture is partly recycled for the own energi requirements of the process during the regenerating process and is delivered via an inlet (17) having a fan (12) to a heating battery (13) for pretreatment of the gas mixture injected to the treatment chamber (16) having filterbeds lying in the same via a chamber (9), said gas mixture treats the concentrated filterbeds individually and consecutively for regenerating in at least one closed secton of the treatment chamber (16) to leave the concentrated gases thereafter to at least another closed section in the treatment chamber (16) before these are led further via heating in the heating battery (10) for catalysating and that the individual filterbeds are screening off individually from each other by automatically regulated throttles within the treatment chamber (16), characterised in that the filter (1) comprises filterbeds formed into cassette modules (15), said cassette modules (15) constitute acute angle relatively each other and are mutually orientated in providing of a maximum filter surface having a very little gas resistance and pressure drop.

2. A method according to claim 1, characterized in that a re-establishment of the pretreatment of the filterbeds occurs in connection with terminated regeneration by that treatment soluton is injected individually or together into the filterbeds by aid of pulverizing injection nozzles and in proportion to regenerating amount of the filterbeds and simultaneous cooling to achieve perfect taking up in the filterbeds.

3. A method according to any preceding claim, characterized in that the regenerated filterbeds are individually blown onto and regenerated automaticly to that level predetermined in advance, whereafter next filerbed is regenerated and so on.

4. An apparatus for decreasing energy consumption and pressure drops when cleaning extensive air volumes containing low concentrations pollutants of hydrocarbons, which during a first phase are caught in an active-coal or a metal filter alternatively a honeycombed vessel surface covered by active-coal or any other adsorbent and said hydrocarbons during at least a consecutive phase are released and converted by a conventional catalyst (11) into carbondioxid and water comprising a filter (1) changeable to a treatment chamber (16), said filter is mountable in line in a ventilation system for process air and is upstreams and downstreams provided with chambers (9) having throttles (8), a catalyst (11) connected to one chamber (9) of said treatment chamber (16) via a heating battery (10), said catalyst via an inlet (17) having a fan (12) constitutes a mainly closed circuit back to the other chamber (9) of the treatment chamber (16) via a heating battery (13) intended to pretreating of the gas mixture which is injected into the treatment chamber (16), characterized in that the filter (1) comprises filterbeds formed in cassett modules (15), said cassett modules (15) constitute acute angle in relation to each other and are mutually orientated, whereby a maximum filter surface having very little gas resistance and pressure drops is achieved.

5. An apparatus according to claim 4, characterized in that the filterbeds mainly consisting of high active coal are prepared with inhibitor solutions, solutions of hydroquinone, tertiary butyl catechol or similar compounds which delay or prevent polymerisation of styrene or its compounds and solvent chemical reactions and thereby make it possible to catch and concentrate with consecutive regene- ration.

The present invention relates to a method and an apparatus for cleaning extensive air volumes containing low concentrations of pollutants of hydrocarbons, with which method and apparatus the hydrocarbons are caught during a first phase in an active carbon or a metal, filter alternatively a honeycombed vessel surface covered by active carbon or any other adsorbent, whereafter during the consecutive phase the caught hydrocarbons are released and converted in a conventional catalyst 11 to carbondioxid and water. The apparatus comprising of one, in a ventilation system for the process air mounted filter 1, which by use of a trottle 8 can be sealed off from the process air and thereby create mainly a closed circuit, where the filter 1 is converted to a mixing chamber 16 connected to a heating battery 10 which in turn is connected to a catalyst 11 for further transport of the cleaned air mixture via an inlet 17 containing a fan 12 and a heating battery 13 and back to the filterbeds existing in the mixing chamber 16 in order to recondition the same.