CN111836997A - A method of generating heat in a power plant - Google Patents

Abstract

A method of generating thermal energy from a hydrocarbon-containing fuel. According to the method, fuel is burned in a combustion device at an elevated temperature, the heat obtained from the combustion is recovered, and the exhaust gases and soot particles produced by the combustion are cleaned by catalytic exhaust gas combustion. Fuel and air are fed into the exhaust gas of the present invention to form a gas mixture which is then subjected to catalytic combustion at temperatures above 600 ℃ to reduce nitrogen oxides and oxidize carbon monoxide, hydrocarbons and soot particles. The method can be used for remarkably reducing the emission of NOx, CO and VOC in gas. The thermal energy generated by the catalytic combustion process may also be used to generate heat, in which case the feed of fuel is divided between the combustion device and the catalytic combustion device.

Description

A method of generating heat in a power plant

technical field

The present invention generally relates to reducing emissions of combustion gases in energy installations. The present invention also relates to heat production in boilers, gas turbines, diesel engines and similar power plants.

In particular, according to the preamble of claim 1, the invention relates to a method for catalytic purification of hydrocarbon-containing energy devices containing nitrogen oxides, carbon monoxide, hydrocarbons and soot particles of combustion gases.

According to the preamble of claim 19, the invention also relates to a method for generating heat with a hydrocarbon-containing fuel. According to this method, the fuel is combusted at an elevated temperature, the heat generated by the combustion is recovered, and the exhaust gas and soot particles generated by the combustion are purified by catalytic exhaust gas combustion.

Background technique

In order to limit the greenhouse effect, emissions of nitrogen oxides (NOx), carbon monoxide (CO), carbon dioxide (CO ₂ ) and hydrocarbons (VOC) from energy production are limited globally. In Europe, several directives for this have been issued for thermal boilers, process equipment, fireplaces, etc. In these directives, emission limits are set for greenhouse gases, either directly or by means of efficiency or emission limits. In the United States, the EPA and CARB set limits on nitrogen oxides and hydrocarbons and their compounds. China is also developing accordingly. For example, in Beijing, the NOx emission limit for boilers is 30 mg/m ³ and the CO limit is 80 mg/m ³ . Such a strict limitation cannot be achieved by existing conventional thermal combustion devices without post-treatment. The same strong tightening trend will continue in other industrialized regions of China.

Before the above-mentioned emissions restrictions, Beijing had already begun to prepare for stricter restrictions. The limit target for NOx is zero, and even for CO, the target limit is significantly lower than the previous limit.

Commercial manufacturers of ultra-low NOx and NOx-free burners use flue gas recirculation, water emulsification and gas preheating in place of flue gas post-treatment in high-efficiency hybrid burners. Despite the burner's NOx-free designation, none of the thermal burner manufacturers have achieved zero NOx emissions. The lowest reported NOx emission was 6ppm accompanied by an _O2 content of 3%.

Another option is the purification of flue gas. Generally, selective catalytic reductants and non-catalytic reductants are used for the removal of nitrogen oxides (hereinafter, selective catalytic reduction, abbreviated as "SCR", and selective non-catalytic reduction, as "SNCR"). In the best case, catalytic SCR can achieve a 90-% purification level at a temperature of about 350°C. In its report, the EPA states that SCR has an average NOx conversion rate of 85%. With a non-catalytic SNCR device, the purification effect was reduced by about 20%. Their use has been directed towards diesel vehicles.

However, SCR units require separate reductant, urea or ammonia and their dosing equipment, which leads to large investment and operating costs. Urea is decomposed in a catalyst to produce ammonia (NH ₃ ) and carbon monoxide (CO). Ammonia and urea are transported and stored in aqueous solutions. The ammonia content was 27% and the urea content was 32%. Ammonia is a highly toxic gas. With SCR equipment, NOx emission levels of around 7–30 ppm can be achieved. In addition, the limitation of CO emissions requires a separate oxidation catalyst. The use of ammonia as a reducing agent is based on its ability to selectively reduce NOx in lean gas mixtures.

Ammonia (NH3) or urea required for selective catalytic reduction as a reducing agent, as well as expensive storage, dosing, heat transfer and reduction equipment, all contribute to the high cost of SCR technology. Additionally, the EPA estimates a 3-year replacement interval for the SCR catalyst. Among SRC catalysts, the most commonly used active material, ie, the catalyst, is vanadium pentoxide (V ₂ O ₅ ), which tends to have the greatest noble metal toxicity. The SCR catalyst is large because of its low space velocity, ie 10000-20000 1/h. The space velocity of the noble metal catalyst is 5...10 times larger than that of the noble metal catalyst, that is, the size of the noble metal catalyst is about one-fifth to one-tenth that of the SCR catalyst.

Other weaknesses of SCR catalysts are NH ₃ leakage (2–5 ppm) and risks during handling and transportation due to NH ₃ toxicity. In the United States in particular, it is required to replace toxic SCR catalysts (V ₂ O ₅ ) with, for example, non-toxic zeolites.

There are also restrictions on so-called catalyst poisons, which must not be contained in the combustion gases. The most important of these are silicones, heavy metals and phosphorus compounds, which permanently deactivate the catalyst. Sulfur-containing compounds do not damage platinum-activated catalysts, but can cause corrosion if the sulfuric acid produced in the reaction concentrates on heat exchanger surfaces above 100°C.

US 4118171, US 2017/153024 and US 2009/284013 are available as prior art publications.

SUMMARY OF THE INVENTION

The present invention seeks to obviate at least some of the problems of the prior art and to provide a completely new method for generating thermal energy from hydrocarbon-containing fuels and, accordingly, for catalytic purification of energy using hydrocarbon-containing fuels The unit produces exhaust gas containing nitrogen oxides and carbon monoxide, hydrocarbons and soot particles.

In the first embodiment of the present invention, the exhaust gas of the energy plant is directed to an exhaust gas burner, where these gases are catalytically oxidized and reduced to reduce the NOx, CO, VOC and particulate content in the exhaust gas and simultaneously generate thermal energy. Typically, NOx compounds are first reduced, and then CO, VOC compounds and particulate impurities in the gas are oxidized while generating recoverable heat energy.

In a second embodiment of the invention, thermal energy is generated from at least two units. When thermal energy is generated in an energy plant by burning fuels with hydrocarbons, the heat is recovered, for example, in a heat exchanger. Fuel and air are fed into the combustion exhaust gas to form a gas mixture, which is then catalytically combusted at high temperature.

By performing combustion in the presence of a catalyst under reducing and corresponding oxidizing conditions of at least 600° C., nitrogen oxides contained in the flue gas are reduced and carbon monoxide, hydrocarbons and soot particles are oxidized. The heat obtained from catalytic combustion is also recovered.

More specifically, the method of the invention is mainly characterized by what is stated in the characterizing part of the independent claims.

Significant advantages are obtained using the present invention.

As mentioned above, it is not possible to generate as clean thermal energy as Beijing now requires using thermal combustion or existing flue gas cleaning methods. However, this goal can be achieved using the method of the present invention, which can reduce NOx, VOC, CO and particulate flue gas emissions even from already operating boilers, diesel and gas turbine power plants to almost zero through catalytic flue gas combustion. At the same time, it can also burn small soot particles produced by oil and gas boilers and diesel engines.

With the aid of the present invention, a method has been created which uses a single device to purify NOx, CO, HC and particulate matter from thermal power plant emissions more efficiently than using any existing production technology, while generating additional energy. Using the method of the present invention, all the emissions listed above can be eliminated in a single plant.

Thus, using the method of the present invention, NOx compounds can be reduced to less than 1 ppm residual, and CO and VOC compounds can be oxidized to less than 2 ppm residual. Small soot particles can also be combusted in flue gas burners at temperatures of 600°C or higher. The preferred temperature range for the burner is 850-1000°C. Within this range, soot particles also burn quickly.

The energy produced at the same time also enables the use of flue gases from thermal boilers, turbines or diesel power plants etc. as a cooling and heat transfer agent in catalytic combustion. The inert thermal mass of the exhaust gas and flue gas is then used for combustion to control temperature and transfer heat. By means of the flue gas, the temperature can be kept within desired limits, preferably in the range of 850-1000°C.

Unlike other cleaning methods, the method of the present invention can be used to increase the heat production capacity of thermal boilers by up to 60%.

Flue gas burners can be added to all energy-generating installations in which sulphur and particulate emissions are low and in which there are no so-called catalyst poisons, on the other hand, NOx, CO and VOC emissions from energy sources No practical significance. In re-combustion, small soot particles produced by, for example, oil-fired boilers and diesel power units are also combusted, unless there is a storage POC catalyst or filter connected to the catalyst, it is best to lay an intermediate device before heat recovery, In this intermediate device, the particles have time to burn before energy recovery.

The particles of diesel engines are mainly small so-called nanoparticles. More than 90% of them have diameters less than 50 nm. They get into the lungs by breathing air and partly through them into the short blood circulation, causing mass deaths. Nanoparticles contain carbon, water, hydrocarbons, and often sulfur, and small amounts of other compounds. They are very porous. Once the hydrocarbons and sulfur-containing compounds are oxidized and the water evaporated, carbon ignites and burns rapidly on all surfaces, while gaseous compounds are slower. Exhaust gas temperatures in the above range (850-1000°C) are favorable for these reactions, especially the combustion of carbon.

Existing, older, more polluting energy production equipment can be raised to new, more stringently required levels of emissions using exhaust gas burners.

In principle, since catalytic combustion operates below the LEL limit, exhaust gas burners can be used in combination with boilers or heat exchangers to remove all gases containing NOx, CO and VOC emissions. This does not present the same safety risks as thermal boilers, where the combustion of volatile organic compounds has led to fatal accidents.

Since, in particular, the amount of gaseous emissions is of little significance with regard to the operation and cleaning results of the exhaust gas burner, there is freedom in the adjustment of the energy source and the choice of the installation. The boiler does not require expensive low NOx or ultra-low NOx burners, and the air-fuel ratio can be optimized for maximum output. In diesel engines, exhaust gas recirculation (EGR) or very lean mixing ratios are not required to reduce NOx emissions and the like.

Exhaust gas burners are also suitable for energy installations that do not meet increasingly stringent emission standards. Investments in reducing emissions are often worthwhile because these devices have a long lifespan and require significant investment. New equipment has new uses.

In the following, the invention is described in detail with the aid of the description of the drawings.

Figure 1 shows a flow chart of one embodiment,

Figure 2 shows a flow chart of the second embodiment,

Figure 3 shows a flowchart of the third embodiment, and

FIG. 4 shows a flowchart of the fourth embodiment.

Detailed ways

In this context, "energy plant" mainly refers to a combustion plant that generates thermal energy or heat, which generates energy from hydrocarbon-containing fuels by means of boilers, diesel engines or gas turbines.

In a first embodiment, the term "carbon-containing fuel" refers to a fuel comprising compounds containing primarily, but not necessarily only, carbon and possibly hydrogen, such as hydrocarbons. In addition to hydrocarbons, the fuel may also contain oxygenates such as ethers, esters and alcohols. Examples of carbonaceous fuels described in the first embodiment are oil, gasoline, diesel and natural gas.

In a second embodiment, the term "carbon-containing fuel" also refers to fuels containing carbon-containing compounds, such as hydrocarbons substituted by these groups, primarily comprising alcohol (hydroxy) groups, ether groups or ester groups, or combinations thereof. These fuels are various biofuels produced from biomass of cultivated plants such as lignocellulose, vegetable oils and animal fats.

The expressions "CO" and "VOC emissions" and the corresponding "NOx emissions" and "soot emissions" refer to the amounts (by mass) of CO, VOC and NOx gases and corresponding soot particles contained in the exhaust gas ).

A "rich" fuel/oxygen (or fuel/air) mixture contains a larger stoichiometric amount of fuel (relative to oxygen), while "lean" contains a smaller stoichiometric amount of fuel.

The present invention provides a method of treating exhaust gas and producing energy using a catalytic exhaust gas burner. As described in more detail below, the method can be used to generate heat and purify exhaust gases.

In this method, additional air and fuel are supplied to the exhaust gas produced in the thermal combustion to form the quantity of gas mixture required for catalytic combustion, and the resulting gas mixture is then passed to the catalytic combustion zone for combustion. The heat from combustion is recovered. The result is a significant reduction in CO, VOC, NOx and soot particulate emissions from catalytic combustion exhaust gases.

In one embodiment, the exhaust gas, fuel and air are homogeneously mixed together to form a homogeneous gas mixture.

In this embodiment, additional air and fuel may be supplied to the exhaust gas burners, and their supply may be controlled by controlling the temperature after the catalyst and linear oxygen sensor according to the desired air/fuel mixture ratio for each catalyst .

In order to carry out the reactions described below, it is most appropriate to add as much fuel as possible to the exhaust gas to form a rich mixture or to achieve a stoichiometric ratio. In the former, only NOxs are reduced to nitrogen ( _N2 ) and oxygen ( _O2 ), while in the latter, CO and VOCs are additionally oxidized to carbon dioxide ( _CO2 ) and water ( _H2O ).

When the reaction is run as a rich mixture, the use of a second catalyst is most appropriate if the required amount of additional air feed is provided to the lean mixture. Best results are obtained using separate oxidation and reduction steps.

In addition to fuel, air must be injected into the flue gas if the maximum amount of clean energy is to be generated. The temperature must be appropriately limited to about 1000°C in order to prevent nitrogen oxides from being produced in the afterburning. Unlike other cleaning methods, this method can increase the heat production capacity of thermal boilers by up to 60%, which is described in detail below.

In one embodiment, fuel and air are mixed in nested perforated feed tubes and static mixers to form a well mixed gas mixture.

Static mixers can be used to ensure homogeneity of the gas mixture, particularly preferred to ensure homogenous combustion.

In one embodiment, catalytic combustion is carried out in one or more stages under reducing and correspondingly oxidizing conditions.

In one embodiment, catalytic combustion is carried out in at least two stages to reduce in particular nitrogen oxides and oxidized carbon monoxide, hydrocarbons and soot particles.

In one embodiment, catalytic combustion takes place in a three-way catalyst of oxidation and reduction catalysts. Catalytic combustion of the gas mixture, for example in a three-way catalyst at a stoichiometric oxygen/additional fuel ratio in the combustion unit, to oxidize unburned CO and VOC compounds in the combustion unit and reduce NOx emissions and oxidize soot particles.

If burned at temperatures above 600°C, the soot particles will also burn.

Alternatively, in the reduction section of the two-stage catalyst, the rich mixture is used to reduce NOx emissions to nitrogen (N ₂ ) and oxygen (O ₂ ) and to oxidize most of the CO and VOC emissions to carbon dioxide (CO ₂ ) and water (H ₂ O).

After that, additional air is passed through the gas mixture to make it thin, and the resulting mixture is passed through an oxidation catalyst. Among them, the remaining CO and VOC emissions are oxidized. In the following heat exchange stage, the generated thermal energy is utilized, for example by means of welded finned tube radiators in the water, and the exhaust gas is then discharged from the boiler to the chimney, where necessary by means of an extraction fan.

In one embodiment, the gas mixture is combusted in an oxidation and reduction catalyst, first with a rich supplemental fuel/oxygen mixture to reduce nitrogen oxides, and then with a lean supplemental fuel/oxygen mixture to oxidize CO, VOC compounds and Soot particles.

In noble metal catalyst reduction, the reaction chain mainly proceeds through steam reformation and water vapor transfer reactions:

H ₂ O+HC->H ₂ +CO and H ₂ O+CO->H ₂ +CO ₂

Then,

H ₂ +NO _x ->N ₂ +H ₂ O.

Some of these reactions are direct oxidation and reduction reactions.

Catalytic combustion always takes place below the lower explosive limit (LEL). The fuel can generally be the same as in the primary energy production facility.

If the flue gas temperature before catalytic reburning drops below 250°C, and the fuel is natural gas or other fuels with a high ignition point, the catalyst should be constructed as a regenerative or regenerative heat exchanger, such as a metal cross-flow catalyst , or to maintain combustion, a low flash point fuel (such as methanol or ethanol) should be added to the fuel mixture as an auxiliary fuel.

The catalyst surfaces used in the combustion are preferably stable metal oxides, especially oxides with cations of Al, Ce, Zr, L or Ba and containing noble metals such as Pd, Pt, Rh or their mixtures with base metals.

These precious metal catalysts are non-toxic and do not produce toxic compounds in the reaction like conventional SCR catalysts.

Under reducing conditions, or under reducing and oxidizing conditions, the temperature of the catalyst is at least 600°C, especially 850-1000°C.

In three-way catalysts, the space velocity is maintained at 50,000-150,000 1/h, for example about 60,000-100,000 1/h, while in reduction and oxidation catalysts, the space velocity is, for example, about 60,000-200,000 1/h, preferably 70000–150000 1/h.

The present invention is particularly useful where fuel is or has been burned in an oil or gas boiler, gas turbine, diesel engine or similar energy burning device.

In one embodiment, a method is provided for purifying exhaust gas or flue gas and generating clean energy by only one or two stages of catalytic reduction and oxidation. In this method, the flue gas also has the function of thermal combination and transfer. Since catalytic combustion is much faster than thermal combustion, it is preferred to use substantially inert flue or exhaust gases to bind energy. In this way, an excessive increase in temperature can be avoided.

As noted above, in one embodiment, the present technology may be used to generate heat by combustion of a hydrocarbon-containing fuel through at least two stages. In this method, a portion of the fuel is combusted in a first combustion stage of a combustion device to generate heat and an exhaust gas containing oxides of nitrogen and oxygen. Then, the heat and exhaust gases obtained from the first combustion stage are recovered. In the second combustion stage, a second portion of the fuel is fed into the exhaust gas obtained from the first combustion stage. Air is also fed to form a combustible gas mixture. The gas mixture thus obtained is combusted to generate heat and to decompose the oxides of nitrogen and oxygen. As mentioned above, in at least one catalytic zone, reducing conditions are maintained, and under these conditions combustion takes place at temperatures above 600°C.

The heat obtained in the second combustion stage is also recovered.

In one embodiment, in the second combustion stage, 10%, most preferably, 15-80 mol% of the total amount of fuel containing hydrocarbons is combusted. With the aid of this method, a substantial part of the thermal energy other than the main energy source, about 60%, can be generated in the second combustion stage.

In one embodiment, flue gas from a boiler, turbine or diesel engine is used as a coolant and heat transfer agent in catalytic combustion. In the absence of cooling inert additives in stoichiometric catalytic combustion, the model shows that the temperature will rise above 2500°C. This is due to the fact that catalytic combustion is about twenty times faster than thermal combustion. In the above embodiment, the temperature of the catalytic combustion is raised to at least 600°C, but preferably to 1000°C, and the flue gas of the thermal energy device is most suitable for use as an inert heat storage and heat transfer agent to keep the temperature of the catalytic combustion at a predetermined temperature selected temperature range. Studies have shown that the unburned gases contained in the flue gas, such as nitrogen and carbon dioxide, do not react under these conditions, but act as inert components and even heat and prevent uncontrolled temperature rises.

In the above-described embodiment, the thermal energy contained in the combustion-generated gas is recovered. Recovery can take place in at least one heat transfer stage, with thermal energy most preferably being transferred to water, air or other liquid or gaseous medium.

In a second embodiment, the present invention is used to catalytically purify, under reducing and oxidizing conditions, exhaust gas from an energy plant using hydrocarbon-containing fuels, the exhaust gas containing nitrogen oxides and carbon monoxide, hydrocarbons and soot particles . In this method, fuel and air are fed into the exhaust gas to form a gas mixture, and this gas mixture is subjected to one- or two-stage catalytic combustion at temperatures above 600°C to reduce nitrogen oxides and oxidize carbon monoxide, Hydrocarbons and soot particles.

In this way, the gas obtained by catalytic combustion has a NOx emission amount of 1 ppm or less, and a CO and VOC emission amount of up to 2 ppm. Small soot particles also burn at the exhaust burner's preferred temperature of 850–1000°C, as the soot ignites around 600°C and burns at a rate higher than that.

According to one embodiment, the method is implemented as a continuous operating process.

During this continuous operation, hydrocarbons are used as reducing agents and energy sources. Another characteristic of this process is the generation of additional energy.

In one embodiment, the oxidation of the particles and the generation of cleaning energy are achieved at high temperatures (at least 1000 degrees). Both require temperature, and this temperature increases conversion efficiency as both particulate oxidant and energy generator and increases with increasing temperature.

Exhaust gas burners using the same fuel as thermal boilers have several advantages over selective (SCR) or non-selective (SNCR) NOx emission reduction units:

- This is a more efficient remover of NOx, CO and VOC emissions. It can be used to achieve NOx emissions of about 1, and depending on the catalyst used, CO and VOC emissions can reach levels of 2ppm.

- Can be used to burn small soot particles.

- Can be used to increase the heat output of the boiler by about 60%.

- There is no need for a separate additional fuel addition, nor a separate storage and dosing system.

- The noble metal catalyst therein has a longer lifespan than the SCR catalyst, which uses a catalyst (V ₂ O ₅ ) which is less thermally and chemically durable than the noble metal. New alternative SCR catalysts are various zeolites, which are sensitive to sulfur poisoning.

- The size of the SCR catalyst is 5-10 times that of the precious metal catalyst. Their prices are not significantly different, as the difference in size can make up for the difference in unit price. The cost of precious metal catalysts is about 60-70 €/dm ³ and the cost of SCR catalysts is about 10 €/dm ³ .

- EPA has indicated that the NOx removal cost for SCR catalysts is around $1400-2000/ton NOx. The cost of catalytic flue gas burners is greatly reduced. The device is smaller and simpler. The reductant ammonia (NH3) or urea used in the SCR unit is about the same price as the fuel of the present invention, but does not generate usable thermal energy.

- The biggest difference is that using an exhaust gas burner produces more energy at a competitive cost. And as a bonus, NOx, CO and VOC emissions are eliminated without additional cleaning costs.

- Due to high toxicity, ammonia gas is transported and stored as a 27% aqueous solution.

- During SCR reduction, 2–5 ppm ammonia leakage (EPA) occurs, which must be catalytically oxidized.

The present invention is verified in detail below in conjunction with the accompanying drawings.

Figures 1 and 2 show two embodiments, Figure 1 shows a method in which the exhaust gas of an energy plant is mainly purified using a catalytic combustion process, and the fuel in the energy plant (power plant) produces both thermal and electrical energy. For its part, FIG. 2 shows a method in which heat is produced in a thermodynamic plant on the one hand and by a catalytic combustion process on the other hand.

As can be seen in the drawings, reference numerals 10, 20, 30, and 50 illustrate thermally fired boilers, diesel power plants, gas turbines or other such energy or power plants using gaseous or liquid fuels. In the case of FIG. 1 , the fuel is mainly supplied to an energy device in which thermal energy is generated, and furthermore electricity is generated from at least a part of the thermal energy thus generated.

In both figures, the exhaust gas of the energy device is led from the exhaust pipe into the mixing chambers 12, 22, where additional air is blown and injected into the fuel. The mixing chamber may include a distribution network.

In one embodiment, a hybrid honeycomb structure is used. Such examples are the methods disclosed in utility model 10627 or CN205001032. Thus, the distribution network may consist of halved sheets of diagonal corrugated steel, which are folded in half on top of each other or folded with the corrugations intersecting. The split sheets can be fastened to each other at the fold points, for example by resistance welding or brazing. The flow channels formed in each layer of the honeycomb cross each other, which leads to mixing and turbulence at higher flow rates.

In a straight channel honeycomb, the flow is laminar. The dimensionless Sherwood (Sh) number representing mass transfer is about 3 and the flow velocity is 10 m/s. In mixed metal honeycombs, the Sh number is about 10-12.

The gas exiting the mixing chamber flows through the static mixers 13 , 23 to the catalysts 14 , 24 , 25 . Behind the catalyst (in the flow direction of the gas mixture) are a linear lambda sensor (not shown) for measuring and regulating the air/fuel ratio and a temperature sensor for controlling the temperature.

After one or two catalytic converters 14; 24, 25, the gas flows to a connection made, for example, of welded ribbed tubes, or to a plurality of heat exchangers 15, 27, where heat is transferred to water or with for other purposes. Embodiments of the heat exchangers 15, 27 may be welded tubes, eg preferably made of ribbed tubes.

Figures 3 and 4 show the structure of the catalytic combustion system in more detail.

In the figures, primary energy production (eg production using diesel engines, gas turbines or combustion boilers) is marked with numbers 30 and 50, and fuel is fed into the exhaust gas along feed pipes 31,51. To form the gas mixture, air is supplied by fans 37,57. The mixture is directed through static mixers 38, 58 for mixing prior to the catalytic zone. Preferably the mixture entering the catalytic zone is a rich mixture.

In the case of FIG. 3 , the catalytic zone includes a cross-flow catalyst 33 . In the case of Figure 4, the catalytic zone comprises a regenerative catalytic heat exchanger.

The gas mixture flowing from the first catalytic zone 33, 53, which is usually reducing, is directed to a second catalytic zone 35, 55 comprising an oxidation catalyst. Then, additional air is sent to the mixed gas by the secondary blowing fans 39 and 59 .

Before starting, one or more catalysts are usually preheated, for example using a hot fan, gas burner or some other heater, to elevate the reaction temperature.

If the temperature difference between the temperature of the exhaust gas and the ignition point of the fuel is small (<150°C), the first catalyst of the exhaust gas burner may be a conventional straight-tube type catalyst. If the content of carbon monoxide (CO) and nitrogen oxides (NO ₂ ) in the exhaust gas is high, the carbon monoxide will ignite in the catalyst at a temperature of about 150°C and the second oxygen in the nitrogen oxides will easily separate and react violently .

When the temperature of the incoming gas is significantly lower than the ignition point of the fuel used in the catalyst (>150°C), a cross-flow or rotating honeycomb regenerative catalytic heat exchanger 53 is required.

In the device of the present invention, the space velocity in the three-way catalytic converter is 50,000-150,000 1/h, preferably 60,000-100,000 1/h, depending on the fuel. In reduction and oxidation catalysts, the space velocity is 70,000-200,000 1/h, preferably 60,000-1,500,000 1/h.

In the second catalytic zone, the thermal energy of the hot gas obtained is recovered in heat exchangers 36, 56, for example transferred to water. The heat exchangers 36, 56 may be fabricated, for example, from welded tubes, preferably ribbed tubes.

After heat transfer, extraction fans 40, 60 may be provided unless the output of the primary energy device and additional air blower is sufficient to deliver sufficient gas through the device. The exhaust gas, ie the purified exhaust gas, is led from the device to outlet pipes, eg exhaust pipes 41 , 61 .

In one embodiment, the apparatus of the present invention for burning a flowing fuel with hydrocarbons in the presence of oxygen or air, in the order of flow of substances, including the stream of substances to be treated,

- mixing zone, catalytic combustion zone, heat recovery zone and degassing zone, where

- the mixing zone is equipped with a feed port for purified gas, a feed port for fuel and a static mixer for homogeneous mixing of gas and fuel,

- the catalytic combustion zone comprises at least two consecutive combustion zones in the flow direction, in which the first is reducing conditions and the second is oxidizing conditions, and

- The heat recovery zone contains a heat transfer element connected to the catalytic zone to recover the heat released therein.

Example

additional energy production

- Natural gas heating boiler with output power of 60MW

- Exhaust gas input 61.000Nm ³ /h

- Additional air input 35.000Nm ³ /h

- Additional input of natural gas 24g/ ^Nm3 in ^96.000Nm3

- Additional energy from combustion 35.2MW, or 59% (calorific value 55MJ/k)

- If the input temperature is 150°C, the temperature after combustion is 920°C,

- reduce nitrogen oxides

-NOx emission 500mg/Nm ³

-NOx total amount 61.000Nm3/hx 500mg/ ^Nm3 =30.5kg/h

Comparison with SCR units

According to the minimum cost calculated by EPA, the cost reduction of SCR device = 1400 US dollars / ton * 30.5kg/h x 0.98 = 41.8 US dollars / h.

Annual cost of using SCR technology = 8000h/a x $41.8/h = $344.400/a.

If the energy produced by catalytic recombustion is not more expensive than the equivalent energy production, NOx removal from the thermal boiler will cost nothing, i.e. an annual saving of $344.400. At the same time, with two-stage combustion (Figure 4), NOx emissions can be reduced to levels of 1 ppm, and CO and VOC emissions can be reduced to levels below 2 ppm.

In order to achieve the objectives, the invention has the characterizing parts set out in the independent claims.

Industrial Applicability

The method is suitable as a synchronous power cleaner for NOx, VOC and CO emissions from boilers, diesel engines, gas turbines, etc. The method of the present invention is also suitable for burning particles such as solid fuel boilers and diesel engines without any additional equipment or extra cost. It is also suitable for generating additional energy in boilers, diesel engines, gas turbines, etc.

Using the method of the present invention, nitrogen oxides (NOx) can be reduced to less than 1 ppm residual, and carbon monoxide (CO) and hydrocarbons (VOC) can be oxidized to less than 2 ppm residual. These values can be achieved even with high primary energy emissions. Small soot particles can also be combusted in the exhaust gas burner, so the particulate filters of boilers and diesel engines can be replaced using the method of the present invention.

According to the method of the present invention, primary energy devices do not require low NOX or ultra-low NOX burners, and diesel engines do not require EGR or very low mixing ratios to reduce NOX emissions. The output of the primary energy device can be maximized. In addition to this, up to about 60% additional thermal energy can be generated using the method of the present invention from the primary energy source. This is especially true when the exhaust gas produced in the first combustion is used as a cooling and heat exchanger in the catalytic combustion, and when fuel is fed into the exhaust gas for the catalytic combustion in the second stage.

Description of reference numerals

10 Primary energy production

11 Generator

12 Distribution network

13 Static mixer

14 Three-way catalytic converter

15 Heat Exchanger

20 Primary energy production

22 Distribution network

23 Static mixer

24 Reduction catalyst

25 Air distribution network

26 Oxidation catalyst

27 Heat Exchanger

30 Primary energy production

31 Feed tube

32 Concentrated Mixtures

33 Cross-flow catalytic converter

34 Dilute mixture

35 Oxidation catalyst

36 heat exchanger

37 Fan

38 Static mixer

39 Secondary fan

40 vacuum fans (if needed)

41 Outlet pipe (exhaust pipe)

50 Primary energy production

51 Feed tube

52 Concentrated Mixtures

53 Regenerative catalytic heat exchanger

54 Dilute mixture

55 Oxidation catalyst

56 Heat Exchanger

57 Fan

58 Static mixer

59 Secondary fan

60 vacuum fan (if needed)

61 Outlet pipe (exhaust pipe)

Reference publications

Patent Literature

US 4 118 171

US 2017/153024

US 2009/284013

Claims (25)

1. A process for the catalytic purification, under reducing and oxidizing conditions, of a combustion gas containing nitrogen oxides and carbon monoxide, hydrocarbons and soot particles, produced by an energy plant using a hydrocarbon-containing fuel,

fuel and air are fed into the exhaust gas, forming a gas mixture, and

-the gas mixture is subjected to one or more stages of catalytic combustion at a temperature above 600 ℃ to reduce nitrogen oxides and oxidize carbon monoxide, hydrocarbons and soot particles.

2. The method of claim 1, wherein the emission level of NOx gases obtained from catalytic combustion is 1ppm or less and the emission level of CO and VOC is at most 2 ppm.

3. The method as claimed in claim 1 or 2, wherein the catalytic combustion is carried out in a catalyst maintained at a temperature of 850 ℃ and 1000 ℃.

4. The method according to any one of claims 1-3, wherein the gas mixture is combusted in a three-way catalyst at a stoichiometric oxygen/extra fuel ratio for the oxidation of CO and VOC compounds not combusted in the combustion device, the reduction of NOx emissions and the oxidation of soot particles.

5. A method according to any one of claims 1-4, wherein the gas mixture is combusted in a redox catalyst, first a rich additional fuel/oxygen mixture is used for reducing nitrogen oxides and then a lean additional fuel/oxygen mixture is used for oxidizing CO and VOC compounds and soot particles.

6. The process according to claim 4 or 5, wherein the space velocity of the three-way catalyst is 50000-1500001/h, preferably 60000-1000001/h, and the space velocity of the reduction and oxidation catalyst is 60000-2000001/h, preferably 70000-1500001/h.

7. The process according to any one of the preceding claims, wherein the catalytic combustion is carried out in at least two stages under reducing and corresponding oxidizing conditions.

8. A method for producing thermal energy from a hydrocarbon-containing fuel, in which method,

-the fuel is burnt in the combustion device at an elevated temperature,

the heat generated by the combustion is recovered, and

the burnt exhaust gases and soot particles are cleaned by catalytic exhaust gas combustion,

it is characterized in that the preparation method is characterized in that,

fuel and air are fed into the exhaust gas to form a mixture, and

-catalytic combustion of the gas mixture at a temperature of at least 600 ℃, preferably above 600 ℃, to reduce nitrogen oxides and oxidize carbon monoxide, hydrocarbons and soot particles.

9. The process according to claim 8, wherein the catalytic combustion is carried out in one or more stages, preferably at least two stages, under reducing and corresponding oxidizing conditions.

10. The method of claim 8 or 9, wherein the exhaust gas, fuel and air are uniformly mixed together in a nested, perforated feed tube and static mixer to form a gas mixture.

11. The method according to any one of claims 8-10, wherein the gas mixture is catalytically combusted in a three-way redox catalyst.

12. The method according to any one of claims 8-11, wherein the gas mixture is combusted in the three-way catalyst at a stoichiometric oxygen/extra fuel ratio for oxidizing unburned CO and VOC compounds in the combustion device, reducing NOx emissions and oxidizing soot particles.

13. The method according to any one of claims 8-11, wherein the gas mixture is first combusted in a rich additional fuel/oxygen ratio mixture in a redox catalyst to reduce nitrogen oxides and then combusted with a lean additional fuel/oxygen ratio mixture to oxidize CO and VOC compounds and soot particles.

14. The process as claimed in any of claims 8 to 13, wherein the temperature in the catalyst under at least reducing conditions or under reducing and oxidizing conditions is 850 ℃ > 1000 ℃.

15. The process as claimed in any of claims 8 to 14, wherein the space velocity of the three-way catalyst is 50000-1500001/h, preferably 60000-1000001/h, and the space velocity of the reduction and oxidation catalyst is 60000-2000001/h, preferably 70000-1500001/h.

16. A method according to any of claims 8-15, wherein the fuel is burned in a combustion device, which is an oil or gas boiler, a gas turbine, a diesel engine plant or a similar energy device.

17. Method according to any of claims 8-16, wherein additional air and fuel are supplied to the exhaust gas burner and the temperature after the catalyst and the linear oxygen sensor are controlled to control their supply in dependence of the air/fuel mixture ratio required by the catalyst.

18. Method for generating heat from fuel with hydrocarbons by at least two stage combustion according to any of claims 8-17, characterized in that it is combined as:

in a first combustion stage, part of the fuel is combusted in a combustion device to produce heat and an exhaust gas containing oxides containing nitrogen and oxygen,

-recovering the heat obtained in the first combustion stage and the exhaust gases separately,

-in a second combustion stage, feeding the off-gas obtained from the previous combustion stage together with a second portion of fuel and air to form a gas mixture,

-the gas mixture thus obtained is subjected to catalytic combustion to generate heat and decompose oxides containing nitrogen and oxygen,

recovering heat obtained from the second combustion stage after combustion at a temperature above 600 ℃ while maintaining reducing conditions in at least one of the catalyst zones.

19. A method according to claim 18, wherein in said second combustion stage at least 10%, most preferably 15-80% of the total amount of hydrocarbon containing fuel is combusted.

20. The method of claim 18 or 19, wherein the primary energy source generates up to about 60% additional thermal energy.

21. The method of any one of claims 8 to 20, wherein the flue gas of the thermal energy device is used as an inert heat storage and transfer agent to maintain the temperature of the catalytic combustion within a preselected temperature range.

22. A method according to any one of claims 8 to 21, wherein the surface of the catalyst used in combustion is a stable metal oxide, preferably the oxide is an oxide in which the cation is Al, Ce, Zr, L or Ba and a precious metal such as Pd, Pt, Rh or a mixture thereof with a base metal.

23. The method of any one of claims 8-22, wherein the noble metal catalyst is non-toxic and does not produce toxic compounds in the reaction as do conventional SCR catalysts.

24. A method according to any of claims 8-23, characterized in that the thermal energy contained in the gases produced in the combustion is recovered in at least one heat exchange stage when transferring the thermal energy to water, air or other liquid or fuel.

25. Use of the method according to any one of claims 1-7 for producing recoverable thermal energy.

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