The invention relates to an apparatus for treating VOC-gases and other combustible gases. The invention relates also to for manufacturing and using such a appa- ratus.

One important object in treating combustible gases is gases comprising VOC. VOC gases are greenhouse gases, which are from a few times to as much as 3000 times more harmful than carbon dioxide (CO2). The (oft-mentioned) rough average is that VOC gases are 11 times worse than CO2 and CH ₄ is 25 times more harmful greenhouse gas than CO ₂ . By calculations it can be shown that carbon cost of VOC-plants is almost always negative, e.g. burned HC have more harmful greenhouse gases even if formed carbon dioxide (CO ₂ ) and power of the plant and building costs of said plant are comprised.

Several practices are available for the reduction of VOC emissions. Useful are wa- ter-thinned or less solvent-based paints and varnishes. VOC gases can be destroyed biologically, they can be recycled, VOC gases can be burned thermally or catalytically, etc. A general trend in emissions is towards lower concentrations, as a result of which the latter techniques are predominant.

VOC gas emissions are characterized by being present in the gas in such a low content which is not nearly enough to generate the energy needed for combustion, but it requires support energy or a highly effective reuse of heat. A regenerative heat exchanger is the most effective apparatus for this purpose. The most common technique is thermal combustion and the next one is catalytic oxidation. Both enable the use of a recuperative or regenerative heat exchanger to increase the heat of a gas arriving at the incinerator. With a recuperative heat exchanger, the efficiency is 75% at its best and with a regenerative one it is as high as 95%. This means that the heat loss with a recuperative heat exchanger is fivefold with respect to a regenerative one, 25% vs. 5%.

The most significant difference between catalytic and thermal combustion pro- cesses is the combustion temperature, which in thermal combustion is about 800°C and in catalytic combustion about 300°C. This means that thermal combustion requires almost three times more energy than catalytic combustion for heating a gas stream. The solvent concentration, which in thermal regenerative combustion is sufficient for generating the energy needed in combustion, is about 1 ,5-3 g/Nm ³ . In catalytic combustion, it is respectively 0,5-1 ,0 g/Nm ³ . This concentration is referred to as the autothermal point (ATP). For the above reason, it has become increasingly popular to turn regenerative thermal oxidizers (RTO) into catalytic oxidizers (RCO) by placing a catalytic converter on top of the heat exchanger. A weakness in regenerative incinerators is that the gas flow direction must be reversed between two accumulator/preheating units (beds). Therefore, during the course of a reversal, a small amount of unpurified gas makes its way into an outlet pipe, thus impairing the incinerator efficiency. The so-called double-bed thermal incinerator is capable of providing a purification efficiency of about 90%. With the catalytic incinerator, due to a smaller size, the reversal-related loss is lesser and thereby the efficiency is higher, generally about 98-99%. The frequently used solution in thermal combustion is a third bed, whereby the efficiency of about 98% can be achieved. The third bed increases costs of the facility by about 30%. It has been proposed that the third bed be replaced by various storage tanks for eliminat- ing the reversal time emission. However, those have not become significantly popular.

Another problem with thermal combustion is . the formation of nitrogen oxides (NOx) at a high temperature as oxygen in the air reacts with nitrogen in _. the air. The standards of NOx emissions are also becoming more demanding from a pre- viously often used limit of 50 mg/Nm3 to as low as 5 mg/Nm3, which is no longer possible to reach by thermal combustion without a gas post-treatment with selective reduction (SCR). In catalytic oxidation occurs no formation of nitrogen oxides.

Description of the invention

What has now been invented is a treatment apparatus for VOC-gases and other combustible gases, which is technically highly beneficial. The invention relates also to for manufacturing and using such a apparatus. In order to accomplish this objective, the invention is characterized by what is presented in the independent claims. Some preferred embodiments of the invention are presented in other claims. In order to accomplish this objective, the invention is characterized by what is presented in the independent claims. Some preferred embodiments of the invention are presented in other claims.

The apparatus according to the invention comprises/is provided with in the gas flow direction at least one gas blower, at least one gas inlet portion, at least two treatment portions each provided with at least one heat exchanger and catalytic converter for the catalytic combustion of e.g. VOC-containing gases, as well as at least one outlet portion. Between the inlet portion and the treatment portions there are at least two direction control valves for alternately conducting the gas to vari- ous treatment portions, and that between the treatment portions there is at least one connecting portion for conducting the gas between the treatment portions, and that each treatment portion has at least one gas discharge control valve for conducting the gas to the outlet portion.

According to one object of the invention, in the at least two treatment portions, the catalytic converters are/have been arranged to be in a direct proximity of the connecting portion linking the same for passing the gas by way of the connecting portion directly from one catalytic converter to the other catalytic converter or vice versa, (claim 2)

According to one object of the invention, the at least two treatment portions com- prises/is provided with comprise a separate gas dispensing chamber having the direction control valve connected thereto.

According to one object of the invention, the at least two treatment portions comprises/is provided with comprise a separate gas dispensing chamber having the gas direction control valve and the discharge control valve connected thereto. (claim 4)

According to one object of the invention, the at least two treatment portions comprises/is provided with comprise a separate gas dispensing chamber, which in vertical direction is disposed in a bottom part of the treatment portions, and that the connecting portion linking these two treatment portions is in vertical direction dis- posed above the treatment portions.

According to one object of the invention, at least one gas treatment portion comprises/is provided with a heating element, such as a heating resistor or a burner, a heating resistor for the direct heating of flowing gas.

According to one object of the invention, the apparatus comprises/is provided with at least one connecting portion fitted with a heating resistor or other heating device for the direct heating of flowing gas. According to one object of the invention, the connecting portion comprises/is provided with a separate gas bypass valve for conducting the gas from the connecting portion to the outlet portion.

According to one object of the invention, the apparatus comprises/is provided with a particle filter for treating the incoming gas.

According to one object of the invention, an external surface of the apparatus is (provided) gastight to the outside.

According to one object of the invention, the gas direction control valves and the gas discharge control valves are (provided) gastight to the outside. According to one object of the invention emissions of the apparatus (PA) can be eliminated by backward circulation or storing to zeolite or absorbent carbon. Said apparatus can comprise e.g. zeolite or absorbent carbon stock for eliminating emissions during reversing of said apparatus by recirculating or stocking.

According to one object of the invention the apparatus can be used without extra energy with VOC-concentration 0,5-1 g/Nm ³ . Real value of autothermal point is 0,5-1 g/Nm ³ . Lower limit is achieved with high energy HC having ignition temperature 270 °C. ATP can also be expressed as follows: ATP = 25 kJ/Nm3, when incoming temp, is 20 °C, ignition temperature <280 °C. E.g. ATP = 0,5 g/Nm3, when VOC is xylene or toluene, I.e. HC having heat of combustion about 50 MJ/kg and most often 20 °C and 280 °C. With low energy, e.g. formaldehydes, alcohols, etc. the value is near 1 ,0 g/Nm ³ , when energy content is 25 kJ/Nm ³

The reactor frame, which is capable of having all of the foregoing functions accommodated therein, is according to the invention possible to make of two welded sections. A bottom section of the reactor frame preferably accommodates the inlet portion, the direction control valves, the heat exchangers and catalytic converters. A top portion of the reactor accommodates the electrical resistors or the burner and the bypass valves. The purpose of this is to provide a reactor which is extremely gastight, compact in size, and technically preferable to manufacture. Prior to reaching a joining seam between the reactor sections, the gas has already trav- eled once through the catalytic converter and 95-98% of the emissions have become purified, which is why a possible leak in the seam is not relevant,

Penetrations for the pneumatically operated valve stems of the reactor are according to one object of the invention made completely gastight with a new type of structure (fig. 3). The shaft seals for conventional penetrations have always some leakage.

The gastight structure makes it possible to place a blower safely upstream of the facility where the gas temperature is low. A blower located downstream of the fa- cility enables leakproofness to be achieved by means of a vacuum generated in the reactor, but the problem is a higher gas temperature, which increases the volume of air and sets special requirements for the blower. Even as low as 300°C doubles the volume of gas, which entails the doubling of a blower size and the use of an expensive specially designed blower. Leakproofness is a principal demand e.g. for a VOC incinerator because several gases to be oxidized are much more hazardous than carbon monoxide. For example, the MAK8 value for carbon monoxide is 30 ppm, for benzene 1 ppm, and for formaldehyde 0,3 ppm. That is, formaldehyde is a hundred times more dangerous than carbon monoxide. The new technical solutions presented in the invention improve cleaning efficiency of the facility, reduce costs, and improve maintainability of the apparatus. According to one object of the invention cleaning efficiency of said apparatus is over 99,5 %.

The essential changes to similar type earlier models comprise, among others, new measurement principles for the facilities, the elimination of a reversal time emission, and the possibility of using simultaneously both metallic and ceramic catalytic converters or heat exchangers to increase the cleaning and transfer of heat efficiency and to decrease acquisition and operating costs.

According to one object of the invention gas fluid in said apparatus (PA) is ar- ranged so that Nusselt number is 6 or higher. In thermal and catalytic incineration facilities, both in the heat exchanger and in the catalytic converter, the gas flow is laminar. At the flow rates used in reactors, the Nusselt and Sherwood numbers are about 3 in the straight channels of an RTO. These grow slowly almost linearly as the flow rate increases. At respective flow rates in mixing channels of the inven- tion, the numbers are respectively 9-12. That is, the relative heat and mass transfer efficiency increases by 3-4 times. The multiplication of flow rates may provide an increase in straight channels to 10-15 and in mixing channels to as high as 100. In the apparatus of the invention Nusselt number is in practical conditions e.g. preferable 9-12. The apparatus can be designed e.g. so that with full capacity and standard products Nu is 12, when flow rate is app. 5 m/s. With partial loadings Nu is lower. But it is important that Nu can be raised in the apparatus by adding flow rate e.g. to 20 m/s. In that case Nusselt number is many deca, e.g. 50-100, potentially even over 100. Now press loss is equivalent^ increasing, but this possibility is the property of this technics and it can be in certain circumstances be very advantageous. Straight channels don't practically have this at all.

The point of departure for new measurements has been a reduction of the reac- tor's cross-sectional area (30-60%), an increase of the reactor's height (30-60%) with respect to prior known regenerative catalytic facilities. The increase of pressure loss caused by these changes is directly proportional to both of the above- mentioned changes. The increase of pressure loss can be offset by increasing the corrugation height or the hydraulic diameter of an opening. The decrease of pres- sure loss is inversely proportional to the second power of the hydraulic diameter, i.e. for example increasing the diameter to a double would decrease the pressure loss to a fourth. It has been possible to calculate with a modeling program that the foregoing changes improve remarkably the efficiency of heat transfer. This is principally due to the fact that a reduction of the cross-sectional area results in a linear increase of the flow rate, which, in a mixing channel according to the invention, enhances exponentially the Nusselt number which represents the heat transfer efficiency. This enables a simultaneous utilization of two nonlinear phenomena to enhance the efficiency of a catalytic converter and a heat exchanger without increasing the pressure loss of the facility. In a similar manner, the mass transfer is enhanced in a mixing catalytic converter.

While the cross-sectional area of a reactor is reduced, the height of a catalytic converter is increased in such a way that the catalytic converter maintains its capacity and turnover rate constant.

In a regenerative incinerator facility of the invention, the oxidation of various VOC concentrations can be carried out automatically. If it has an autdthermal point of 1 g/Nm3, the facility functions thereby without additional energy. If the concentration rises to 7 g/Nm3, the facility begins to heat up whereby the automatic reversal temperature control shall prolong the reversal interval to 60 > 300 seconds. This lowers the efficiency of a heat exchanger, such that temperature does not rise in the reactor's top compartment beyond a given threshold value of e.g. 600°. If the concentration keeps growing, the hot gas bypass valve shall open and allow some of the gas past the heat accumulation type heat exchanger. However, the bypass flow is limited to not more than 50%, thereby maintaining the reactor in a hot condition. If temperature keeps nonetheless rising, all directional valves shall be opened and the gas is allowed to proceed past the reactor. If all the gas is allowed to discharge by way of a hot gas bypass channel, the heat accumulating side of the reactor shall cool down and the reactor becomes more difficult to control.

In the new structure, a metallic heat exchanger is constructed from prefabricated modules of e.g. 300 mm x 300 mm x150 mm (WxLxH). These modules are stacked in such a way that the sheets of a module extend at a 90-degree angle with respect to the orientation of the preceding level. Thereby is obtained a remarkable homogenization of flow distribution because, in a static mixer, the flow may also proceed in lateral direction in response to pressure differences and an open inter-channel connection. The flow distribution is effectively homogenized by this and by the smaller cross-sectional area while the amount of untreated gas is reduced during a, reversal of direction. The facility can now be conveniently installed in a container. Delivery time of standard apparatus can preferably by only 2 months.

The VOC incinerator facility, which is constructible from just a few standard mod- ules and a few modular frames, can be assembled in a few days with standard components suitable for all size categories having been prefabricated in advance. By virtue of this, the construction schedule is particularly short. At first has been plant series of seven standard apparatus, which series can be completed with similar bigger or smaller apparatus. Standard apparatus are even more than .50% smaller than smallest rival apparatus in the market. Six apparatus with capacity 1300 Nm ³ /h and two apparatus with capacity 5000 Nm ³ /h can be transported in 20 feet sea container.

Apparatus are fully ready for installation automatic apparatus, which only need incoming and outgoing pipes and el and compressed gas connections. According to one object of the invention, the treatment apparatus has at least three parallel reactors and gas dispensing valves for alternately dispensing the supply gas to regenerative heat exchangers so as to minimize the loss during a reversal of direction. According to one object of the invention, the gas is directed upstream of a reactor through an activated carbon or zeolite storage into the reactor for the duration of a reversal of direction, whereby the reversal of direction can be conducted with clean air without the VOC gas. The hydrocarbon accumulated in activated carbon or zeolite is desorbed with hot air conducted from a top portion of the reactor and the gas is delivered to the front of a main blower. This enhances operation of the apparatus even further.

According to one object of the invention, both direction control valves of the reactor's inlet side are closed for a brief period (about 2 s) and, during this period, the unpurified gas is blown with compressed air or a high performance blower through the heat exchanger and catalytic converter of the reactor's inlet side. This is followed by reversing the direction of flow. Thereby, the reversal time emission is successfully eliminated.

With each of the foregoing solutions it is possible to eliminate reversal time emis- sions so as to reach the purification degree of over 99,5%.

According to one object of the invention, the oxidizing catalytic converter for gases is a ceramic catalytic converter and it contains precious metals, basic metal oxides and/or other catalytic compounds.

According to one object of the invention, the oxidizing catalytic converter for gases is a metal core catalytic converter and it contains precious metals, basic metal oxides and/or other catalytic compounds.

The ceramic heat exchanger can be a monolithic honeycomb with holes or a structure assembled from discrete mixing pieces. The catalytic converter may also be a structure stacked from circular ceramic pellets. The catalytic converters are coated with a high surface area coating, having one or a few platinum group metals impregnated therein, the latter being catalyst poisons resistant to high temperatures and catalytically active and long-standing.

The use of ceramic materials enables the treatment of acids and halogenated hydrocarbons. When being burned, the halogenated hydrocarbons may develop so- called supertoxins, dioxins, furans and acids. In thermal combustion there is required a temperature of 900-950°C to preclude the formation of supertoxins. In catalytic combustion there is required a correct type catalytic converter with the temperature being about 400°C. The apparatus according to the invention may comprise not only an oxidizing catalytic converter but also a selective catalytic converter (SCR). It is advisable to place the SCR catalytic converter above the oxidizing catalytic converters as in that case the gas travels first through an oxidizing catalytic converter, in which some of the incoming nitrogen oxides (NO) become oxidized into nitrogen dioxides (NO2), thus expediting substantially the reduction process of nitrogen oxides. As the gas passes onto the other side of the reactor, there is first another SCR catalytic converter to complete the reductions, and then downstream thereof an oxidizing catalytic converter which oxidizes not only the residual VOC-compounds but also possible leftover ammonia. In this case, it is preferable to use in the oxidizing catalytic converter a platinum-containing catalyst.

In SCR-catalyst alternative reaction chains are:

- NO + NH ₃ -> N ₂ + H ₂ O (low, space velocity n. 12.000 1/h)

- NO + NO ₂ + NH ₃ -> N ₂ + H ₂ O (fast, space velocity n. 20.000 1/h)

- NO ₂ + NH ₃ -> N ₂ + H ₂ O (lowest, space velocity n. 10.000 1/h)

With the mechanism described earlier fastest reaction chain is achieved. Boilers and combustion engines produce nitrogen monoxide (NO). With platinum aluminum oxide part (about. 30 %) of nitrogen monoxide (NO) can be burned to nitrogen dioxide (NO2). SCR-catalyst can be installed directly to replace oxidizing catalytic converter. Same speeding cannot be achieved but to reaction mechanism but it is more simple and cheaper solution. In that case urea could be supplied to inlet pipe after the gas blower.

VOC-burning plant can be used in this target also because it has efficient regener- ative heat exchanger, it is needed especially when installing SCR-plant to old power plants because those have outlet gas temperature often at the level 110- 150 °C, which is not sufficient for reduction reactions of SCR-catalyst. Those need 250-300 °C.

Because of efficient heat exchange power of rising the temperature can be low- ered by 90%. By this possible changes and economizers nowadays used for energy recirculation can be avoided

Advantages of VOC-burning apparatus comprise also burning of carbon monoxide (CO) and hydrocarbons (HC) and compact structure of apparatus. By and large, the facility according to the invention has a blower located upstream of the reactor, wherein the air to be treated is colder and whereby the size and power demand for a blower are lesser than those for blowers installed downstream. The catalytic VOC incinerator facility can be used for oxidizing actual hydrocarbons and several other harmful substances, such as carbon monoxide, hydrogen sulfide, alcohols, and the like. The facility can also be supplemented with an SCR catalytic converter to reduce nitrogen oxides. Since harmful substances are generally present in such a low concentration that direct combustion is not possible without support energy, the facility has an effective regenerative heat exchanger. Standard facilities are installed in containers for shipping to the destinations thereof and for providing there permanent shelters for the incinerator facilities.

Next will be described one operating system for an apparatus of the invention. There, the VOC-containing gas comes from a factory along a pipe to an incinerator facility. The gas arriving at the reactor has its rate of flow controlled with a vacuum sensor, which uses a frequency converter to adjust the rotational speed of a blower. The gas arrives at the blower through a particle filter, after which the gas proceeds to the reactor's inlet portion and further by way of a heat exchanger to the first catalytic converter. The gas warms up in the accumulation type heat ex- changer to the operating temperature of a catalytic converter, after which the catalytic converter oxidizes a predominant fraction (>95%) of the VOCs or other combustible gases. Thereafter, the gas passes by way of a connecting portion to the other side of the reactor and proceeds first through a catalytic converter and a heat exchanger (= heat accumulator) to a discharge control valve in the gas dis- pensing chamber of the second section and further by way of the outlet portion into an exhaust pipe.

Once the gas is heated in the inlet side accumulator to the operating temperature, the accumulator shall cool down until the gas does not reach a desired reaction temperature. At this time, the temperature sensor supplies a message about this to a control logic, which maneuvers the directional valves to a new position effecting a reversal of the flow direction in the reactor. Now, the preceding accumulator begins heating the supply gas.

If the energy content of a gas is high, the reactor starts heating too much. If temperature in the top portion of a reactor reaches an established upper limit, the temperature sensor will send a message to the control logic which issues an in- struction to open the bypass valve. Once temperature returns to below the limit value, the hot gas bypass valve will close.

A cold facility is activated with energy produced by electrical resistors or a burner by using a predetermined running cycle. Specific description of the invention

The apparatus according to the invention has negative carbon cost, e. g. it is important carbon sink. An example as follows describe the situation:

Capacity 30.000 Nm ³ /h

Hours 8700 h/a

VOC gas and concentration Methane 1g/Nm3 = 261 t/a

GWP100 value of methane 25 (CO ₂ equivalent 25x261 = 6525 t/a)

Autothermal point 0,85 g/Nm3 (no need for extra energy)

Gas blower, power 75 kW

Balance:

Incoming CO2 (2,75x261 t/a) 718 t/a

Gas blower (0,8x75 kWx0,32 kg/kWhx8700h) 167 t a

Buildings, steel (19 t x 0,85 kg/kg /12a) 1 ,4 t/a

Apparatus and it's maintenance 1 , 6 t/a

Produced CO ₂ 888 t/a

CO ₂ produced by the apparatus in a year 1776 t a Equivalent reduction of CO ₂ by methane burning -6524 t/a

Carbon cost -5636 t/a

Said example apparatus has thus capacity of 5635 t carbon dioxide in a year, which is same amount of carbon dioxide as 2000 cars (140 g/km x 20.000 km/a) annually produce.

Importance of VOC-emissions could be expressed by comparing them to CO ₂ emissions of cars. If all VOC-emissions of the world (app. 100 Mt a) would be burned catalytically, carbon sink of 2150 Mt/a would become, which is app. as big as CO ₂ -emission produced by all 700 million cars (20.000 km/a, 150 g/km). of the world. Some embodiments of the invention are described in the subsequent example. Fig. 1 shows a vertical section view of an apparatus placed in a container for treating VOC-gases. Fig. 2 shows a horizontal section view of the apparatus according to fig. 1. Fig. 3 shows a direction control valve useful in an apparatus for treating VOC-gases.

An apparatus PA according to fig. 1 and fig. 2, which is set up in a container 1 , comprises in a gas flow direction at least one gas blower 4, one gas inlet portion 5a, and two treatment portions 7-8 each provided with at least one heat exchanger 7a and catalytic converter 8a for the catalytic combustion of VOC-gases, as well as one outlet portion 2. The apparatus PA has a particle filter 3 for treating the incoming gas. Between the inlet portion 5a and the treatment portions 7-8 are two direction control valves 6 for alternately conducting to various treatment portions 7- 8, and between the treatment portions 7-8 is a connecting portion 9 for conducting the gas between the treatment portions 7-8, and each treatment portion 7-8 has a gas discharge control valve 11 for conducting the gas to the outlet portion 12. In the two treatment portions 7-8, the catalytic converters 8a are arranged to be in a direct proximity of the connecting portion 9 linking the same for passing the gas by way of the connecting portion 9 directly from one catalytic converter 8a to the other catalytic converter 8a or vice versa. The outlet portion 12 features an outlet fitting. In the apparatus PA of fig. 1 and fig. 2, the two treatment portions 7-8 comprise a separate gas dispensing chamber 5b having the gas direction control valve 6 and discharge control valve 11 connected thereto. The gas dispensing chamber 5b is in vertical direction disposed in a bottom part of the treatment portions 7-8, and that the connecting portion 9 linking these two treatment portions 7-8 is in vertical direction disposed above the treatment portions. The connecting portion 9 has _. a heating resistor 9b for the direct heating of flowing gas e.g. in connection with a startup. The connecting portion 9 features a separate gas bypass valve 10 (not visible in fig. 2) for conducting the gas from the connecting portion 9 directly to the outlet portion 12 e.g. due to a process adjustment or malfunctions. The apparatus has a separate control unit 2 for controlling the apparatus in terms of its operation. The apparatus PA has its external surface designed to be gastight to the outside. E.g. the direction control valves 6 and the discharge control valves 11 , as well as the bypass valve 10, are gastight to the outside.

Fig. 3 shows a direction control valve 6 gastight to the outside, which is connected to the gas inlet portion 5a and to the gas dispensing chamber 5b, between which is a wall 5e provided with a tight-fit gas flow opening 5f. The valve 6 has a pneu- matic cylinder 21 provided with a seal 22a and an attachment cylinder, as well as with a slide bearing 24. The valve 6 is further provided with a coupling seal 22b for connecting the valve 6 in a gastight manner to an outer wall 5c of the gas inlet portion 5a. In addition, the valve 6 has a disc valve 25 controlled by a pneumatic cylinder 22 for regulating the gas flow between the gas inlet portion 5a and the gas dispensing chamber 5b.

The construction and configuration setup of a valve 6 as shown in fig. 3 can also be applied in the bypass valve 10 and the discharge control valves 11 depicted in fig. 1.

Some practical VOC-apparatus is described in following table 1. Table 1 : Standard VOC products

Explanation.

Table 1 : Standard VOC products

Type type marking

Capacity Nm3/h maximum capacity

Dim. WxL dimensions of cross-section of reactor and catalyst, mm Catalyst vol. dm3 catalyst volume

Power kW power of additional and start-up heating

Container type of transport and operation frame

ATP g/Nm3 autothermal point, grams of solvent in standard cubic dP Pa pressure loss of reactor in autothermal point on maximum lo; HE kg weight of heat exchanger, kg