Method and apparatus for reducing contaminants of combustible gas

Abstract

A method (100) for reducing pollutants of a combustible gas (G), comprising: generating (S101) a lean mixture (GM) comprising at least air (A) and a combustible gas (G); fully oxidizing (S102) the lean mixture (GM) by a catalytic process (CP) during a first operating phase (P1) to obtain an exhaust gas (EG); generating (S103) a rich mixture (GM) comprising at least air (A) and a combustible gas (G); and partially oxidizing (S104) the rich mixture (GM) by a catalytic process (CP) during a second operating phase (P2) to obtain a clean combustible gas (CG) preferably for the production of heat and power.

Description

Technical Field

[0001] The present invention relates to a method for reducing pollutants in a mixed gas containing a combustible gas in particular. The present invention also relates to a corresponding apparatus for using the above method and a system including the apparatus.

Background Art

[0002] Biomass gasification technology is based on a thermochemical process that converts dry solid biomass such as wood and agricultural waste into a combustible gas. This combustible gas, also known as wood gas or synthesis gas, can be used as fuel for an internal combustion engine (ICE), and its chemical energy is converted into mechanical, electrical, and thermal energy.

[0003] Synthesis gas usually has a lower heating value (LHV) in the range of 4 - 6 MJ / Nm3 and is thus typically defined as a low heating value fuel. Furthermore, the gas composition may change during operation according to the thermochemical conditions of the gasification reactor and the quality of the biomass fuel itself.

[0004] An important critical matter regarding synthesis gas produced from biomass gasification is that it is essentially contaminated by polycondensable organic compounds called tars. The average tar concentration can vary in the range of 0.1 - 50 g / Nm3 depending on the reactor technology employed. The tar concentration strongly depends on two stages during which the gasification system operates, namely the start - stop stage and the steady - state stage.

[0005] During the start - up and shut - down stages, since the tar concentration in the wood gas is high, the gas is not suitable for combustion in an ICE. Therefore, the gas is generally transferred to a secondary combustion facility typified by a flare stack. The purpose is to completely burn the gas to meet the emission levels required by regulations.

[0006] During the steady state phase, since the tar concentration in the wood gas is low (but not zero), the gas is transferred to the ICE and used as fuel to produce power and heat output. Since the tar concentration is a critical matter important for the operation of a durable and reliable ICE, contaminants are usually removed by specific filtration equipment.

[0007] Many prior art solutions for reducing contaminants in combustible gas were either expensive (especially with regard to operating costs) or complex because they used systems consisting of several parts and components.

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, an object of the present invention is to provide a method and an apparatus for reducing contaminants in combustible gas, which can be easily implemented and can efficiently generate clean combustible gas used for the production of heat and electricity and other purposes.

Means for Solving the Problems

[0009] This object is solved by a method for reducing contaminants in combustible gas, the method comprising generating a lean mixture gas comprising at least air and combustible gas, and completely oxidizing the lean mixture gas by a catalytic process during a first operating phase to obtain an exhaust gas. The method also comprises generating a rich mixture gas comprising at least air and combustible gas, and partially oxidizing the rich mixture gas by a catalytic process during a second operating phase to obtain, preferably, clean combustible gas for the production of heat and electricity.

[0010] This allows a catalytic process using a corresponding single catalytic device to be used as a pollutant removal approach in two different operating stages. In particular, in the first operating stage, the mixed gas is completely combusted by oxidation with the catalyst, and in the second operating stage, the mixed gas is purified by the catalytic process, i.e., the pollutants are reduced. The catalytic devices used in the oxidation processes in the two operating stages are essentially the same, but the process conditions are different. In fact, in the first operating stage, the catalytic process is carried out on a lean mixed gas, while in the second operating stage, the catalytic process is carried out on a rich mixed gas. Advantageously, by using the same catalytic device to completely oxidize the mixed gas in the first stage and remove pollutants in the second stage, this method can reduce both the operating costs and capital expenditure of a system that requires the purification of combustible gas by pollutants.

[0011] Lean combustion or lean burn refers to the combustion process of gas in an internal combustion engine or a general combustion chamber in a state of excess air (when considered as the ratio of air to combustible gas). On the other hand, rich combustion or rich burn refers to the combustion process of gas in an internal combustion engine or a general combustion chamber in a state of insufficient air (when considered as the ratio of air to combustible gas).

[0012] According to an embodiment, the combustible gas can be synthesis gas generated by a gasification process in a gasification system or a gasification device. For example, the synthesis gas can be wood gas. The first operating stage can correspond to the start-up stage and / or the shutdown stage of the gasification system, and the second operating stage can be the steady-state stage of the gasification system. In particular, in a lean mixed gas, the ratio of air to combustible gas is higher than 1, and in a rich mixed gas, the ratio of air to combustible gas is lower than 1. Thereby, complete oxidation is carried out by the catalytic process during the start-up stage and / or the shutdown stage of the gasification system, and pollutant removal by partial oxidation is carried out by the catalytic process during the steady-state stage. As a result, clean gas is generated and can be used for supply to an internal combustion engine.

[0013] In particular, the air excess coefficient λ can be defined as the ratio of the actual air-to-combustible gas ratio of the mixed gas to the stoichiometric air-to-combustible gas ratio. That the air excess coefficient λ is greater than 1 means that there is too much air. On the other hand, that the air excess coefficient λ is less than 1 means that there is not enough air for all the combustible gas to burn.

[0014] The pollutant to be treated according to this method can be tar in the combustible gas. The high temperature of the rich mixed gas by the catalytic process during the second operation stage can determine the decomposition of the pollutant, i.e., tar. According to the decomposition of the pollutant, i.e., tar, long-chain hydrocarbons are decomposed into simpler molecules such as light hydrocarbons.

[0015] The method of the present invention can also be advantageously used in other industrial processes and petroleum and natural gas processes that are not necessarily related to biomass gasification. This method can be used in all systems that generate waste gas streams with a temporally variable composition according to the process operating parameters.

[0016] The method includes the step of controlling the oxidation of the lean mixed gas and / or the rich mixed gas over the operating period. In other words, unlike the prior art solution of obtaining uniform spatial oxidation along the catalyst surface of the reactor by varying the oxidation radially in the reactor, in this method the oxidation varies with time. This makes it possible to cope with transient operating periods (start-up and shutdown) with low gas quality. During this period, complete oxidation is considered to have a positive effect, while in other periods (for example, the steady-state stage), complete oxidation is considered to result in energy losses. Here, the expression "complete oxidation" is intended to mean that all the necessary oxygen can be used (neither more nor less) for combustion. If the oxygen is only spatially distributed (as is usually the case in the prior art) and not temporally distributed while being spatially uniform (as in this method), combustion can occur even if the necessary oxygen is in a smaller amount (for example, half) or a larger amount (for example, double).

[0017] This method is a dual-purpose solution process in which control of a catalytic process, such as catalytic oxidation during the first stage, or control as pollutant removal during the second stage, is obtained by adaptive regulation of the air flow.

[0018] Thus, in an embodiment, the method includes the step of actively regulating the air flow during the first operating stage and / or the second operating stage, wherein the air flow during the first operating stage is different from the air flow during the second operating stage. In particular, the method can include the step of automatically switching between a first air flow mode during the first operating stage and a second air flow mode during the second operating stage.

[0019] As will be explained in more detail below, air flow control essentially serves to maintain the temperature within a predetermined range of values between the first and second operating stages. In the first operating stage, in order to oxidize the combustible elements of the combustible gas and reduce the pollutant content, the gas is completely oxidized using a catalytic process on a catalyst substrate. This oxidation is carried out in a lean combustion mixture (λ > 1), where the air injected at this time is in excess of the stoichiometric amount. Air injection control is optimized to dilute the mixed gas and keep the optimum oxidation temperature within a predetermined range, for example, 450 - 550 °C. The best result of catalytic oxidation is a completely oxidized gas with a minimum pollutant compound concentration and as a result, a small environmental impact. The gas generated by the catalytic process in the first operating stage is discharged outside the system and is not used for heat and power production, but complies with the exhaust gas emission regulations. In the second operating stage, the purpose of the catalytic process is to reduce the proportion of pollutants (e.g., tar). In order to reduce the concentration of pollutants, the injected air is set lower than the stoichiometric ratio (λ < 1). Also in this stage, air injection is controlled to optimize the partial oxidation of the mixture and keep the optimum temperature within a predetermined range, for example, 450 - 550 °C. The best result of catalytic conversion is a gas with a low pollutant concentration and a high residual heat content, which is suitable for heat and power production by, for example, an internal combustion engine or other devices.

[0020] In one example, the method further includes actively adjusting the air flow between a minimum value and a maximum value, where the minimum value corresponds to zero air insertion. In particular, the method can further include switching between a reducing air flow mode without air insertion and an oxidizing air flow mode with air insertion during the first operating stage and / or the second operating stage. The adaptability to switch from a (i.e., reducing) air flow mode without air insertion to an (i.e., oxidizing) air flow mode with air insertion is considered important in gasification. In fact, gas parameters (i.e., temperature, lower heating value, etc.) change during the operating time. This gives added value to the method compared to other methods of the prior art.

[0021] According to an embodiment, the method includes adjusting the air flow during the first operating stage to maintain a ratio of air to combustible gas higher than 1, preferably between 3 and 5, and most preferably equal to 4.

[0022] According to an embodiment, the method includes adjusting the air flow during the second operating stage to maintain a ratio of air to combustible gas lower than 1, preferably between 0 and 0.5, and most preferably equal to 0.3.

[0023] To control the temperature change during the catalytic process, in an embodiment, the method includes measuring the temperature value of the mixed gas after the mixed gas has been oxidized by the catalytic process. In particular, it is necessary to maintain the temperature value during the catalytic process within a predetermined range, i.e., between a minimum temperature value Tmin and a maximum temperature value Tmax. The minimum temperature value Tmin is the temperature at which the pollutants begin to decrease. For example, it is the temperature at which long-chain hydrocarbons begin to decompose into simpler molecules such as light hydrocarbons. It is clear that at temperatures lower than Tmin, the pollutant concentration does not decrease and the catalytic process has no effect on gas purification. This temperature value can depend on the type of pollutants and the catalyst material used in the catalytic process.

[0024] The maximum temperature value Tmax is the melting temperature of the catalyst substrate used in the catalyst process. At temperatures higher than Tmax, it is obvious that the catalyst device used in the catalyst process can no longer be used and the oxidation process does not occur. Before reaching the melting temperature, the device can reach the so-called material stress temperature Tstress. The material stress temperature Tstress is the temperature at which the catalyst material begins to deteriorate so as to reduce the performance of the catalyst device used in the catalyst process. Therefore, the temperature value during the catalyst process needs to be maintained within the range of Tmin and Tmax, preferably within the range of Tmin and Tstress, with Tmin < Tstress < Tmax. According to an embodiment, the temperature value during the catalyst process needs to be maintained within the range of 400°C and 550°C, where Tmin is about 400°C, Tmax is about 550°C, and Tstress is about 500°C.

[0025] When the temperature value is higher than the maximum temperature value (Tmax), the method includes the step of controlling the air flow. As described above, the maximum temperature value (Tmax) is the melting temperature of the catalyst substrate used in the catalyst process. When the temperature value is lower than the minimum temperature value (Tmin), the method includes the step of operating the heating process and setting the control hysteresis to a predetermined temperature range (Trange). As described above, the minimum temperature value (Tmin) is the temperature at which the pollutants begin to decrease. According to an embodiment, Tmin is about 400°C, Tmax is about 550°C, and Trange is between 400°C and 450°C.

[0026] In one aspect of the present invention, an apparatus for reducing pollutants in combustible gas is provided. This apparatus is preferably used in the method according to one of the above-described embodiments.

[0027] This device comprises a housing having an inlet region for receiving a mixed gas containing at least air and a combustible gas, an outlet region for discharging a gas with reduced pollutants, and a catalyst region located downstream of the inlet region and upstream of the outlet region for partially or completely oxidizing the mixed gas by a catalytic process, and the housing is removably insertable into a gasification system. In particular, in a first operating stage, the catalyst region is configured to completely oxidize the mixed gas, and in a second operating stage, the catalyst region is configured to partially oxidize the mixed gas. Also, in the first operating stage, the mixed gas is a lean mixed gas and the ratio of air to the combustible gas is higher than 1, and in the second operating stage, the mixed gas is a rich mixed gas and the ratio of air to the combustible gas is lower than 1.

[0028] Advantageously, the device is a catalytic device, in particular a catalytic converter. Compared to prior art systems that perform catalytic techniques in complex reactors, the method of the present invention uses a device that is easier to use and more compact. In fact, the present device is equivalent to a commercially available (automotive) catalytic device and has a housing that allows for easy attachment and / or removal to the gasification system. As a result, the present device is compact, inexpensive (both in terms of OPEX and CAPEX), adaptable, and easy to maintain.

[0029] In an embodiment, the catalyst region comprises a catalyst substrate, which is preferably a multi-stage assembly. The material of the catalyst substrate is generally a platinum group metal (ruthenium, rhodium, palladium, osmium, iridium, platinum), nickel, and rhenium. Regarding the structure of the catalyst region, any structure that maximizes the contact between the catalyst material and the pollutants can be used, but other design elements such as thermal expansion and mechanical durability must also be considered.

[0030] The device further comprises an air inlet disposed in the inlet region and a gas inlet disposed in the inlet region away from the air inlet, and the air inlet is coupled to a fan element.

[0031] Furthermore, the device can be provided with a control device for switching between a first operating stage of discharging the gas discharged from the outlet region to the outside and a second operating stage of preferably using the gas discharged from the outlet region for the production of heat and electricity. The first and second operating stages respectively correspond to the aforementioned first and second operating stages in which the mixed gas is completely oxidized or partially oxidized.

[0032] According to an embodiment, the control device can be configured to control the air flow and / or control the temperature value during the catalytic process.

[0033] In order to maximize the mixing of air and combustible gas in the mixed gas, the device can further be provided with a swirling induction element arranged in the inlet region. In particular, the swirling induction element can be arranged in the space located between the inlet region and the catalytic region.

[0034] In order to measure the temperature value of the mixed gas, the device is provided with at least one temperature transducer. The temperature transducer can be connected to the control device and can be arranged upstream and / or downstream of the catalytic region.

[0035] In order to measure the pressure value of the mixed gas, the device is provided with at least one pressure transducer. The pressure transducer can be connected to the control device and can be arranged upstream and / or downstream of the catalytic region.

[0036] In order to measure the composition of the mixed gas, the device is provided with at least one gas composition sensor. This sensor can be connected to the control device and can be arranged upstream and / or downstream of the catalytic region.

[0037] In order to measure the ratio of air to combustible gas, the device is provided with a lambda sensor connected to the control device. The lambda sensor is preferably arranged downstream of the catalytic region.

[0038] In order to change the temperature, the device is provided with a heating element connected to the control device. In particular, the heating element is arranged in the catalytic region in contact with, for example, the catalytic substrate used in the catalytic process.

[0039] According to an embodiment, the components of the device can be made from, without limitation, stainless steel AISI409 for the piping and from, without limitation, 1.4767 (CrAI6) for the catalyst substrate used in the catalyst process.

[0040] In another aspect of the present invention, a system, particularly a gasification system, is provided. This system comprises a device according to any one of the above-described embodiments.

[0041] The method and device of the present invention are a technique or system for removing contaminants having a dual purpose in different operating stages.

[0042] During the first operating stage, for example, during the start-up and / or stop stage of the gasification system, the main purpose is to avoid the presence of a free flame by reducing the temperature when oxidation occurs due to the use of the catalytic device. In this operating stage, advanced combustion control is established by a control system capable of producing a stable reaction during the LHV oscillations of the wood gas. This control is obtained by actively adjusting the air injection flow into the range of λ>1 (lean combustion conditions). Thereby, the volume of the exothermic (high-temperature) region is reduced, and the combustion is maintained within a sealed volume suitable for the indoor environment.

[0043] During the second operating stage, for example, during the steady-state stage in the gasification system, the main purpose is to convert contaminants (e.g., tar) into lighter combustible gases. In this operating stage, advanced control of contaminant conversion is established by an active control system capable of adjusting the air injection into the range of λ<1 (rich combustion conditions). Thereby, the overall reliability of the system, such as the gasification system, is improved, and the need for maintenance is reduced.

[0044] During the first operating stage (i.e., the start-up and / or shutdown stage), the control of the oxidation process is established by a combination of controlling the optimum conversion temperature by an external heater and directly controlling the air injection flow. When the second operating stage (i.e., the steady-state stage for thermoelectric power supply) begins, the same device changes its goal to partial combustion in order to reduce pollutants. The goal of the first operating stage is to release the calorific value regarding the combustible mixture by complete combustion of the gas, while the goal in the second operating stage is to keep the calorific value of the gas as constant as possible and at the same time remove pollutants (tar) to make the gas suitable for, for example, ICE.

[0045] In the figures, the subject matter of the present invention is schematically shown, and elements of the same or similar action are usually given the same reference numerals.

Brief Description of the Drawings

[0046]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 3C

Figure 4A

Figure 4B

Figure 4C

Figure 4D

Figure 5

Figure 6A

Figure 6B

Embodiments for Carrying Out the Invention

[0047] Referring to FIG. 1, a method 100 for reducing contaminants in a combustible gas G is shown in a schematic flowchart. The method 100 provides different steps based on the operating stages at which the method 100 is executed. By operating stage is meant the mode of operation of a system, such as a gasification system, used to process the combustible gas G.

[0048] In step S101, a lean mixed gas GM is generated. This mixed gas GM includes at least a combination of air A and combustible gas G. The lean mixed gas GM is generated by acting on an air stream, that is, by increasing the amount of air in the mixed gas GM. In step S102, during the first operating stage P1, the lean mixed gas GM is completely oxidized by a catalytic process CP. Specifically, the mixed gas GM is oxidized on a catalyst substrate, and the generated gas is discharged to the outside as exhaust gas EG. During these steps, the air stream is optimized to dilute the mixed gas GM and maintain an optimal oxidation temperature. When the method 100 is used to process the combustible gas G in a gasification system, the first operating stage P1 corresponds to a start-up and / or shutdown stage.

[0049] In step S103, a rich mixture gas GM is generated. This mixture gas GM includes at least a combination of air A and a combustible gas G. The rich mixture gas GM is generated by acting on an air stream, that is, by reducing the amount of air in the mixture gas GM. In step S104, during the second operation stage P2, the rich mixture gas GM is partially oxidized by a catalytic process CP. Specifically, the mixture gas GM is oxidized on a catalyst substrate, and the generated gas is a clean gas CG with reduced pollutants. During these steps, the air stream is controlled to optimize the partial oxidation of the mixture gas GM and maintain an optimal oxidation temperature. This means that the concentration of pollutants is minimized and the combustible gas G can maintain a high residual calorific value. When the method 100 is used to process the combustible gas G in a gasification system, the second operation stage P2 corresponds to a steady-state stage.

[0050] Figure 2 shows the application of the method 100 in two operation stages P1 and P2.

[0051] In the first operation stage P1, the combustible gas G is combined with air A to form a lean mixture gas GM, that is, a mixture gas GM with an air-to-combustible gas ratio higher than 1. This mixture gas GM is completely oxidized by a catalytic process CP, and the obtained exhaust gas EG is discharged into the atmosphere. The exhaust gas EG has no calorific value and cannot be used, for example, for heat production. For example, if the combustible gas G is wood gas with a lower heating value (LHV) of about 5 MJ / Nm3, the exhaust gas EG can have a calorific value close to zero, that is, LHV = 0 MJ / Nm3.

[0052] In the second operation stage P2, the combustible gas G is combined with the air A to form a rich mixture gas GM, that is, a mixture gas GM with an air-to-combustible gas ratio smaller than 1. This mixture gas GM is partially oxidized by the catalytic process CP, and the resulting clean gas CG is a gas with a reduced pollutant concentration. The clean gas CG still has a calorific value and can be used, for example, for heat production and in an internal combustion engine (ICE). For example, if the combustible gas G is wood gas having an LHV of about 5 MJ / Nm3, the clean gas CG may have a slightly reduced calorific value, i.e., LHV = 4 MJ / Nm3.

[0053] Figures 3A to 3C show the details of the apparatus 10 according to an embodiment. The apparatus 10 is configured to be used in the method 100 for reducing pollutants of the combustible gas G as described above. The apparatus 10 basically comprises a housing 30 having an inlet region 12 for receiving the mixture gas GM, an outlet region 14 for discharging the gas, and a catalytic region 16 located between the inlet region 12 and the outlet region 14. The apparatus 10, particularly the housing 30, is configured to be attached downstream of the reactor region of the gasification system and removed from downstream. The catalytic process can be carried out inside this compact apparatus 10 without the need to construct an additional reactor for the gasification system. The attachment of the apparatus 10 to the gasification system occurs by simply connecting the inlet region 12 to the combustible gas G supply line and the air A supply line of the gasification system and connecting the outlet region 14 to the gas outlet line of the gasification system.

[0054] In the inlet region 12, the combustible gas G is premixed with the air A. The structure and length of the inlet region 12 are designed to maximize the homogeneity of the mixture and to avoid, for example, backpressure and backfire phenomena from a combustion part (not shown).

[0055] The catalyst substrate of the catalyst device is arranged in the catalyst region 16. The diameter and length of the catalyst region 16 are optimized to ensure complete conversion according to the residence time of the mixed gas GM in the catalyst device. In the case of a weak chemical reaction, the temperature of the catalyst substrate can be controlled by a heating element 27 that maintains the optimal surface temperature within a predetermined range of values (see FIGS. 6A and 6B in particular).

[0056] In the outlet region 14, the oxidized gas is discharged from the device 10 and transferred to an exhaust device or an engine, such as an ICE, depending on the operating stage of the implementation system. In particular, based on the fact that the device 10 is used during the first operating stage P1 or the second operating stage P2, the gas discharged is either the exhaust gas EG to be discharged to the outside or the clean gas CG that can potentially be used for the production of heat or electricity.

[0057] FIG. 3B is a side view of the device 10, and FIG. 3C represents a longitudinal section of the device 10 of FIG. 3B along line A-A.

[0058] The combustible gas G is injected from the gas inlet 13, and the air A is injected from the air inlet 11 via a fan element 15 (not shown here). The fan element 15 helps to ensure a flow rate that can cover a wide range of air-to-combustible gas ratios (λ) both in the sub-stoichiometric range (λ < 1) and the over-stoichiometric range (λ > 1). The device 10 includes sensor ports 17 arranged both upstream and downstream of the catalyst region 16. The sensor ports 17 are configured to install measuring devices such as temperature transducers, pressure transducers, lambda sensors, and / or gas composition analyzers.

[0059] The device 10 further includes a heating element 27, such as an electrical resistance, installed on the outer surface of the catalyst substrate in the catalyst region 16. The heating element 27 is for ensuring the minimum activation temperature during weak exothermic conditions. The heating element 27 can be controlled by a local controller such as a thermostat or a general system controller such as a programmable logic controller (PLC).

[0060] As is apparent from FIG. 3C, the catalyst substrate can be a multi-stage assembly, which in particular has two stages 18, 19 separated by voids 20. The multi-stage design is employed to ensure an appropriate degree of combustion and residence time for variable combustible gas and air flow rates. In order to ensure higher conversion efficiency at a lower cost, more than two stages can be employed with the goal of increasing the residence time of the gas in the catalyst device. The number of stages and the type of catalyst material can be selected in relation to the required degree of system efficiency.

[0061] Advantageously, the device 10 also comprises a joint 21 located between the inlet region 12 and the catalyst region 16 and between the catalyst region 16 and the outlet region 14. The joint 21 is realized by two annular surfaces connected to each other by connection means such as a plurality of screws, and a seal element is arranged between these annular surfaces. The joint 21 basically serves to remove the catalyst region 16 from the inlet region 12 and / or the outlet region 14. This is extremely useful for the maintenance of the device 10, for example when it is necessary to regenerate or replace the catalyst device used in the catalyst process.

[0062] FIG. 4A shows that the device 10 can additionally comprise a swirl inducing element 22. This element is preferably arranged in the inlet region 12 on the inlet side of the catalyst region 16. Thereby, the mixing of air and combustible gas can be maximized to ensure homogeneous combustion of the mixed gas GM entering the catalyst region 16.

[0063] As shown in FIGS. 4B to 4D, the swirl inducing element 22 is composed of an annular structure 29 and a central spiral structure 24. The annular structure 29 is provided with a plurality of through holes 23 distributed at the edge of the annular structure 29. The swirl inducing element 22 has a protruding rim 25 at the rear (FIG. 4D) for accommodating the spiral structure 24. The through holes 23 serve to fix the swirl inducing element 22 to the device 10 at the joint 21 between the inlet region 12 and the catalyst region 16. At this time, the protruding rim 25 is arranged in the inlet region 12.

[0064] Figure 5 shows the changes in two parameters, namely temperature and air-to-flammable gas ratio, between the first and second operating phases. As described above, these two parameters are controlled according to the air flow.

[0065] In the first operating phase P1, for example, the start-up and / or stop phase, the air flow control is based on adding fresh air. As shown in Figure 5, the minimum air flow rate is adjusted to maintain the air-to-flammable gas ratio λmin equal to 4. When the control temperature exceeds a value of 500 °C, the control device 26 is configured to increase the air flow rate to the device 10, thereby enhancing the dilution of the flammable gas and then reducing the oxidation temperature.

[0066] In the second operating phase P2, for example, the steady-state phase, the control is based on partial combustion. To establish the partial oxidation of the mixed gas GM, the air flow rate is reduced below the stoichiometric value (λ = 0.3). The condition of 500 °C is sufficient for the conversion of pollutants. When the control temperature exceeds a value of 500 °C, the control device 26 is configured to reduce the air flow rate to the device 10, thereby reducing the oxygen for the exothermic reaction and then reducing the temperature.

[0067] By adopting this dual-purpose control method in this hybrid type (for example, both elements can be controlled by a proportional-integral-derivative PID controller as the control device 26), it is possible to control the temperature change to be lower or higher than the target value. Actually, the purpose of this control method is to maintain the optimum temperature (500 °C in the example) for the following reasons. That is, - To ensure the optimum working state of the catalyst substrate of the catalyst device used in the catalyst process CP. The surface of the catalyst substrate is strongly affected by high temperatures. High temperatures can cause early wear and may result in a decrease in both the conversion efficiency and the system life. - To ensure the minimum pollutant concentration during all operating phases (start-up, stop, steady state, partial load, etc.). Different operating conditions may have different pollutant species, and by being able to adjust the temperature accordingly, the highest efficiency of the catalyst system can be adapted to each condition. Ensure combustion safety by keeping the λ control away from an air / fuel gas ratio outside the safe range.

[0068] Figures 6A and 6B are diagrams of the control elements of the device 10 and the corresponding control process 200 for maintaining the temperature within a predetermined range of values. The control elements can include a heating element 27, a fan element 15, and a temperature transducer 28, all of which are connected to a control device 26. The fan element 15 is disposed at the air inlet 11 to manage the air flow within the device 10. The heating element 27 is disposed in the catalyst region 16 of the device 10, for example, on the substrate of a catalyst device used in the catalyst process CP. The temperature transducer 28 is disposed in the outlet region 14 where the temperature of the mixed gas GM is measured after passing through the catalyst process CP. Alternatively, the temperature transducer 28 can be disposed directly on the catalyst surface in the catalyst region 16.

[0069] The heating element 27 is activated when the self - combustion of the fuel gas G with a weak LHV cannot be guaranteed. The control hysteresis can be set in the range of 400 - 450 °C. The air injection flow rate can be controlled by a variable frequency driver (VFD) through a bypass or mechanical system controlled by a valve.

[0070] Referring to Figure 6B, in step S201, the temperature value of the mixed gas GM is measured after the catalyst process CP, for example, by the temperature transducer 28 in Figure 6A. Thereby, the temperature change during the catalyst process CP is continuously monitored.

[0071] If the temperature value is higher than the maximum temperature value (Tmax) (S202), the method includes step S203 of managing the air flow. As already described, Tmax is the melting temperature of the catalyst substrate used in the catalyst process CP, for example 550 °C. The process then returns to step S201 to continuously measure the temperature of the mixed gas GM. In step S204, it is determined that the temperature value is lower than the minimum temperature value (Tmin). In this case, the method includes step S205 of operating the heating process and setting the control hysteresis to a predetermined temperature range. As already described, Tmin is the temperature at which the pollutants begin to decrease, for example 400 °C.

[0072] The process then returns to step S201 to continuously measure the temperature of the mixed gas GM. If the temperature is lower than Tmax and higher than Tmin, the temperature has reached its optimum value and the method is maintained in step S206. Explanation of symbols

[0073] 10 Device 11 Air inlet 12 Inlet region 13 Gas inlet 14 Outlet region 15 Fan element 16 Catalyst region 17 Sensor port 18 Stage 1 19 Stage 2 20 Void 21 Joint 22 Swirl induction element 23 Through hole 24 Spiral structure 25 Protruding rim 26 Control device 27 Heating element 28 Temperature transducer 29 Ring structure 30 Housing 100 Method for reducing pollutants 200 Control process

Claims

Claim 1 A method (100) for reducing pollutants in a combustible gas (G), comprising: generating a lean mixture gas (GM) containing at least air (A) and the combustible gas (G) (S101); fully oxidizing the lean mixture gas (GM) by a catalytic process (CP) during a first operating stage (P1) to obtain an exhaust gas (EG) (S102); generating a rich mixture gas (GM) containing at least air (A) and the combustible gas (G) (S103); partially oxidizing the rich mixture gas (GM) by a catalytic process (CP) during a second operating stage (P2) to obtain a clean combustible gas (CG), preferably for heat and power production (S104); and the method (100) comprising the above steps. Claim 2 The method (100) according to claim 1, wherein: a. the combustible gas (G) is a synthesis gas produced by a gasification process in a gasification system, the first operating stage (P1) corresponds to a start-up stage and / or a shutdown stage of the gasification system, the second operating stage (P2) is a steady-state stage of the gasification system, and b. in the lean mixture gas (GM), the air-to-combustible gas ratio is higher than 1, and c. in the rich mixture gas (GM), the air-to-combustible gas ratio is lower than 1. The method. Claim 3 The method (100) according to claim 1 or 2, further comprising controlling the oxidation of the lean mixture gas (GM) and / or the rich mixture gas (GM) over an operating period. Claim 4 The method (100) according to any one of claims 1 to 3, further comprising: a. actively adjusting an air flow during the first operating stage (P1) and / or the second operating stage (P2), wherein the air flow during the first operating stage (P1) is different from the air flow during the second operating stage (P2), and / or b. automatically switching between a first air flow mode during the first operating stage (P1) and a second air flow mode during the second operating stage (P2). The method comprising the above steps. Claim 5 The method (100) according to any one of claims 1 to 4, further comprising actively adjusting the air flow between a minimum value and a maximum value, wherein the minimum value corresponds to zero air insertion. Claim 6 The method (100) according to any one of claims 1 to 5, further comprising switching between a reducing gas flow mode without air insertion and an oxidizing gas flow mode with air insertion during the first operation stage (P1) and / or the second operation stage (P2).

7. The method (100) according to any one of claims 1 to 6, further comprising a. adjusting the air flow during the first operation stage (P1) to maintain an air-to-combustible gas ratio higher than 1, preferably equal to 4, and / or b. adjusting the air flow during the second operation stage (P2) to maintain an air-to-combustible gas ratio lower than 1, preferably equal to 0.3, The method comprising.

8. The method (100) according to any one of claims 1 to 7, further comprising a. measuring the temperature value of the mixed gas (GM) after the catalyst process (CP) to control the temperature change during the catalyst process (CP), and / or b. maintaining the temperature value during the catalyst process (CP) between a minimum temperature value (Tmin) and a maximum temperature value (Tmax), preferably between 400°C and 550°C, where the minimum temperature value (Tmin) is the temperature at which the reduction of pollutants begins and the maximum temperature value (Tmax) is the melting temperature of the catalyst substrate used in the catalyst process (CP), and / or c. measuring the temperature value of the mixed gas (GM) after the catalyst process (CP) to monitor the temperature change during the catalyst process (CP) (S201), and when the temperature value is higher than the maximum temperature value (Tmax) (S202), the method includes a step of managing the air flow (S203), where the maximum temperature value (Tmax) is the melting temperature of the catalyst substrate used in the catalyst process (CP), preferably 550°C, and when the temperature value is lower than the minimum temperature value (Tmin) (S204), the method includes a step of operating a heating process and setting a control hysteresis within a predetermined temperature range (S205), where the minimum temperature value (Tmin) is the temperature at which the reduction of pollutants begins, preferably 400°C, and the predetermined temperature range is preferably between 400°C and 450°C. The method comprising.

9. An apparatus (10) for reducing pollutants in a combustible gas (G) using the method (100) according to any one of claims 1 to 8, An inlet region (12) for receiving a mixed gas (GM) containing at least air (A) and the combustible gas (G); An outlet region (14) for discharging a gas (EG; CG) with reduced contaminants; A catalyst region (16) located downstream of the inlet region (12) and upstream of the outlet region (14), which partially or completely oxidizes the mixed gas (GM) by a catalytic process (CP); A housing (30) having the above, and the housing (30) is removably insertable into a gasification system; Device (10).

10. The device (10) according to claim 9, which is a catalytic device, particularly a catalytic converter, device (10).

11. In the device (10) according to claim 9 or 10, a. The catalyst region (16) comprises a catalyst substrate, which is preferably a multi-stage assembly, and / or b. The device (10) further comprises an air inlet (11) arranged in the inlet region (12) and a combustible gas inlet (13) arranged in the inlet region (12) away from the air inlet (11), and the air inlet (11) is coupled to a fan element (15); Device.

12. The device (10) according to any one of claims 9 to 11, further comprising a. A control device (26) for switching between a first operating stage (P1) of discharging the gas (EG) discharged from the outlet region (14) to the outside and a second operating stage (P2) of using the gas (CG) discharged from the outlet region (14), preferably for the production of heat and electricity, and / or b. A control device (26) for controlling the air flow and / or controlling the temperature value during the catalytic process (CP), and / or c. A swirling induction element (22) arranged in the inlet region (12) for maximizing the mixing of air (A) and combustible gas (G) in the mixed gas (GM); Device.

13. The device (10) according to claim 12, further comprising a. At least one temperature transducer (28) connected to the control device (26) and arranged upstream and / or downstream of the catalyst region (16), and / or b. At least one pressure transducer connected to the control device (26) and arranged upstream and / or downstream of the catalyst region (16), and / or c. At least one gas composition sensor connected to the control device (26) and arranged upstream and / or downstream of the catalyst region (16), and / or d. A lambda sensor connected to the control device (26) and arranged upstream of the catalyst region (16), and / or e. A heating element (27) connected to the control device (26) and arranged in the catalyst region (16), An apparatus comprising the same.

14. A system, particularly a gasification system, comprising the apparatus (10) according to any one of claims 9 to 13.

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