CN116396783A - Method for partially oxidizing tar in crude gas by dielectric barrier discharge plasma - Google Patents

Abstract

The invention discloses a method for partially oxidizing tar in crude fuel gas by dielectric barrier discharge plasma, which comprises the steps of adding a certain amount of O into the fuel gas containing the tar ₂ Activation of O with dielectric barrier discharge plasma ₂ Producing an active substance with strong oxidizing property, which reacts with tar molecules in a partial oxidation way to convert the tar molecules into CO and H ₂ Meanwhile, the generation of liquid phase and solid phase products is inhibited, tar molecules are recovered while tar is efficiently converted, and the fuel gas is purified while the energy utilization efficiency is improved.

Description

A method for partial oxidation of tar in crude gas by dielectric barrier discharge plasma

Technical field:

The invention relates to the field of biomass gasification crude gas purification, in particular to a method for partial oxidation of tar in crude gas by dielectric barrier discharge plasma.

Background technique:

The raw gas produced by biomass gasification contains a few grams to tens of grams of tar per standard square meter, which is a complex mixture of various condensable hydrocarbons, including monocyclic to pentacyclic aromatic Group compounds, oxygenated hydrocarbons and complex polycyclic aromatic hydrocarbons. Tar is gaseous at high temperature, but it will condense into a viscous liquid when the temperature of the gas is lower than its dew point, which will block and corrode downstream equipment such as pipelines and valves, and affect the stable operation of the system; the tar content in the crude gas is affected by the reactor type and operating parameters , the energy contained in it can account for 5-15% of the total energy of biomass. At low temperature, this part of energy cannot be directly utilized together with the gas, resulting in energy waste. Therefore, an efficient and environmentally friendly tar removal technology is urgently needed at this stage.

The current tar removal technology can be divided into physical removal method, thermochemical method and gas discharge plasma method.

The physical removal method uses physical means, such as water washing, filtration, cyclone separation, etc., to transfer the tar from the gas phase to the condensed phase, thereby removing the tar in the gas. This method is mature in technology, easy to operate, and widely used in actual production, but it cannot recover tar energy, and it will also cause secondary pollution. The thermal cracking method uses the thermochemical conversion reaction of tar at high temperature to generate gas products to remove tar. This method requires high temperature (>1100°C) conditions to meet the removal effect, and the energy consumption is high. The catalytic cracking method reduces the temperature required for tar cracking by introducing a catalyst, and can convert tar into gas products with low energy consumption. At the same time, it can also adjust the proportion of gas components. It is an ideal tar removal method. However, the reaction temperature of this method is still high (>700°C), which easily leads to catalyst sintering; in addition, the tar cracking catalyst is prone to carbon deposition and deactivation.

According to the state of thermal equilibrium, plasma can be divided into thermal equilibrium plasma and non-thermal equilibrium plasma. Among them, non-thermal equilibrium plasma is also called low-temperature plasma. Low-temperature plasma generation methods mainly include electron beam irradiation method and gas discharge method. The gas discharge method is to generate a discharge by applying a strong electric field to break down the gas, and obtain high-energy electrons at the same time. The temperature of the electrons can reach 1-20eV, and the temperature of the gas molecules and ions is close to the ambient temperature. The high-energy electrons generated by the discharge are the root of the chemical reaction. The inelastic collision between the electrons and the background gas molecules produces excited gas molecules, free radicals and ions. These active particles further react with the pollutant molecules to remove the pollutants. According to different discharge forms, gas discharge can be divided into pulse corona discharge, sliding arc discharge, dielectric barrier discharge and so on. The researchers applied low-temperature plasma technology to the steam reforming of tar and _CO2 reforming, and found that this method can effectively realize the conversion of tar, but has the problem of low energy efficiency. Furthermore, coupling the low-temperature plasma with the catalyst can improve the conversion efficiency and energy efficiency, but the existence of the catalyst leads to high reaction temperature (suitable temperature of the catalyst) and low reaction stability (deactivation of the catalyst due to carbon deposition, poisoning, etc.) question.

Therefore, the prior art needs to be improved and developed.

Invention content:

The object of the present invention is to provide a method for partial oxidation of tar in crude gas by dielectric barrier discharge plasma, by adding a certain amount of _O2 to the gas containing tar, and using dielectric barrier discharge plasma to activate _O2 to produce strong oxidizing Active material, the active material undergoes a partial oxidation reaction with tar molecules, converts tar molecules into CO and H ₂ , and at the same time inhibits the formation of liquid and solid phase products, recovers the energy of tar molecules while efficiently converting tar, and improves energy utilization Purify gas while improving efficiency.

The present invention is achieved through the following technical solutions:

A method for partial oxidation of tar in crude gas by dielectric barrier discharge plasma, the method comprising the following steps: the crude gas obtained by gasification of biomass is thoroughly mixed with _O in a gas mixer and then enters a plasma reactor ; Control _O2 and the mass ratio of tar is 1.4～1.7; In plasma reactor, tar, oxygen and fuel gas are under plasma activation at 200-450 ℃ and preferably 300-350 ℃ partial oxidation reaction takes place, and tar Molecules are converted into CO and H ₂ combustible gases to achieve purification of gas.

Preferably, for the raw gas after the dust collector, use a gas chromatograph to analyze the gas composition, calculate the explosion limit range of the gas; and determine the tar concentration by solvent absorption-weighing method.

The gas composition analysis is based on the national standard "GB/T 28901-2012 Gas Chromatographic Analysis Method of Coke Oven Gas Components", and the formula for calculating the explosion limit is Richard Chatley's formula.

The solvent absorption-weighing method selects isopropanol as the tar absorption liquid.

The introduction of O ₂ flow should first ensure that there is no risk of explosion after mixing with gas, and then make corresponding adjustments according to the mass content of tar in the gas. The mass ratio of O ₂ to tar is preferably 1.4-1.7.

The plasma generation method in the plasma reactor is preferably dielectric barrier discharge. Compared with other discharge forms (sliding arc discharge, pulse discharge, etc.), dielectric barrier discharge has high non-equilibrium state, high electron temperature, simple structure and low cost. , stable operation and other advantages. The mixed gas coming from the gas mixer, in the dielectric barrier discharge activation area, O ₂ and N ₂ , CO ₂ , H ₂ and other components in the gas collide with the high-energy electrons generated by the discharge to be activated into a variety of active substances. Such as excited state N ₂ , excited state O ₂ , H free radicals, O free radicals, etc., the above active substances undergo chemical reactions with tar molecules, including cracking reactions, oxidation reactions, etc., and convert tar molecules into combustible gas substances, CO and H _2. Realize deep removal of tar in biomass gasification gas, purify crude gas, and improve energy utilization efficiency.

Further, the energy density of the dielectric barrier discharge is 0.1-1.0 kWh/Nm ³ (based on a tar concentration of 30 g/Nm ³ ), preferably 0.6 kWh/Nm ³ (based on a tar concentration of 30 g/Nm ³ ).

The choice of O ₂ is mainly to improve the tar removal efficiency and energy efficiency, increase the yield of gas products, and inhibit the formation of liquid and solid products. In the dielectric barrier discharge process, compared with water vapor and CO ₂ , the same concentration of O ₂ can obtain a higher concentration of strong oxidizing active species. On the one hand, this can promote the oxidation reaction of tar to generate more gas products; on the other hand, the active material can undergo oxidation reaction with the carbonaceous substances deposited on the inner wall of the reactor, further increasing the yield of gas products and reducing the solid phase Product yield, reduce the adverse effect of solid product attachment on dielectric barrier discharge.

The beneficial effects of the present invention are as follows:

1) The present invention adds a certain amount of O ₂ to the tar-containing gas, and uses dielectric barrier discharge plasma to activate O ₂ to generate active substances with strong oxidative properties, and the active substances and tar molecules undergo partial oxidation and cracking reactions. At a temperature of 300-350°C and without a catalyst, the tar molecules are converted into gas-phase combustible substances of CO and _H2 , while the formation of liquid-phase and solid-phase products is suppressed, and the energy of tar molecules is recovered while efficiently converting tar , while improving the energy utilization efficiency, the deep removal of tar in the raw gas of biomass gasification is realized, and the raw gas is purified.

2) The method does not introduce a catalyst, avoids low stability caused by catalyst deactivation, and can realize long-term stable operation of the equipment.

3) The raw gas of biomass gasification contains high concentrations of H ₂ and CO components. The introduction of O ₂ into the system has the following two problems: causing gas explosion and oxidizing combustible components. The method calculates the gas explosion limit, measures the tar concentration, and determines the concentration of O ₂ added in the gas, so as to realize the conversion of tar into CO and H ₂ and reduce the oxidation of gas components as much as possible while avoiding gas explosion.

Description of drawings:

Fig. 1 is the structural representation of the device that realizes the partial oxidation of tar in crude gas by dielectric barrier discharge plasma;

Among them, 1. _O2 cylinder; 2. _O2 flowmeter; 3. _CO2 cylinder; 4. _CO2 flowmeter; 5. Steam generator; 6. Water vapor flowmeter; 7. Tar injection pump; 8. Gas mixer; 9. Dielectric barrier discharge plasma reactor; 10. Plasma power supply; 11. High voltage electrode; 12. Grounding electrode.

Detailed ways:

The following is a further description of the present invention, rather than a limitation of the present invention.

The device that realizes the method for the partial oxidation tar of dielectric barrier discharge plasma as shown in Figure 1: comprise tar injection pump, O _Steel cylinder, CO _Steel cylinder, steam generator, gas mixer, dielectric barrier discharge plasma reactor, Among them, the gas mixer and the plasma dielectric barrier discharge reactor are connected end to end in sequence, and the _O2 cylinder, the _CO2 cylinder, the tar injection pump, and the steam generator are connected to the gas mixer.

The main body structure of the dielectric barrier discharge plasma reactor is a quartz cylindrical cylinder body with an inner and outer diameter of 25 mm and an inner diameter of 20 mm; a cylindrical solid high-voltage electrode rod made of stainless steel is placed on the axis of the cylinder body, and its diameter is 16 mm; A layer of stainless steel wire mesh is wound on the outer surface of the cylinder, and its length along the axis of the cylinder is 50mm. The electrode rod is connected to the plasma power supply, and the stainless steel mesh is connected to the ground wire to form a dielectric barrier discharge plasma reactor.

Embodiment 1: A kind of method of dielectric barrier discharge plasma partial oxidation tar

Use the device shown in Figure 1, choose N ₂ as the carrier gas, set the tar concentration to 30g/Nm ³ through the syringe pump, close the valve of the CO ₂ steel cylinder, turn off the steam generator, control the O ₂ flow rate through the flow meter, and conduct dielectric barrier discharge The temperature of the reactor is 300° C., and the discharge energy density is 0.6 kWh/Nm ³ .

Including the following steps:

(1) Collect the tar (viscous liquid) produced by the gasification of wood chips, and introduce the collected tar into the gas mixer through the syringe pump. The gas mixer is wound with a heating belt outside, and the temperature is kept at 250 ° C;

(2) Supply O ₂ using a high-pressure oxygen cylinder. Calculate the explosion limit range of the mixed gas in advance to avoid the gas explosion caused by the introduction of _O2 ; set the mass ratio of _O2 to tar as 1.4, select _O2 to pass into the gas mixer, and mix it with the carrier gas and gasified tar After being fully mixed, enter the dielectric barrier discharge reactor;

(3) In the dielectric barrier discharge reactor, O ₂ , tar, carrier gas and plasma react in the reactor.

Comparative example 1:

Referring to Example 1, the difference is that the valve of the _O2 cylinder is closed, the steam generator is turned on, the steam flow is controlled by a steam flowmeter, and the molar flow of water vapor is set to be equal to the molar flow of _O2 in Example 1.

Comparative example 2:

Referring to Example 1, the difference is that the valve of the _O2 cylinder is closed, the valve of the _CO2 cylinder is opened, the _CO2 flow rate is controlled by a CO2 flowmeter, and the molar flow rate of _CO2 is set equal to the molar flow rate of _O2 in Example 1.

In Example 1 and Comparative Example 1 and Comparative Example 2, the tar content was measured by absorption-weighing method, and the gas composition at the outlet was measured by gas chromatography. Utilize this method to measure the tar concentration of the embodiment of the present invention 1 and comparative examples 1 and 2 and the gas composition at the outlet, and the comparison results are as shown in table 1:

Table 1

As can be seen from Table 1, after adopting the device and method in Example 1 of the present invention to carry out the partial oxidation of tar by dielectric barrier discharge, the removal rate of tar and the main products CO, _H and _CO in the tail gas are higher than those of water in dielectric barrier discharge Steam Reforming (Comparative Example 1) and _CO2 Reforming (Comparative Example 2). It can be seen that the dielectric barrier discharge partial oxidation method has good effects in tar removal and combustible product generation (inhibition of liquid phase and solid phase product generation).

Example 2-8

Referring to Example 1, the difference is that the temperature of the plasma reactor, the _O2 flow rate, and the discharge energy density are changed to observe the change of the tar removal rate. When changing a certain condition in the above-mentioned conditions, keep the numerical values of other parameters equal to that of Example 1. The change of tar content before and after purification obtained by analysis is shown in Table 2.

Table 2

It can be seen from Table 2 that the optimal operating temperature range of the plasma reactor is 300-350 °C, above or below this temperature range, will lead to a decline in the removal rate of tar; the optimal operation of the mass ratio of _O2 to tar The interval is 1.4 to 1.7. In this interval, the tar removal rate is stable at about 92%. The tar removal rate increases with the increase of the discharge energy density, and the optimal value is 0.6kWh/Nm3; although the discharge energy density increases When the removal rate is as high as 1.0kWh/Nm ³ , the removal rate increases, but the range is small, which is not conducive to the improvement of energy efficiency, so the optimal value is set at 0.6kWh/Nm ³ .

Example 9

Referring to Example 1, the difference is that the discharge energy density is 1.0kWh/Nm ³ , the carrier gas is replaced by nitrogen gas with simulated gasification gas, and the change of tar removal rate and composition of simulated gasification gas is observed. The changes in tar content before and after purification are analyzed and shown in Table 3.

table 3

Entrance exit Tar, g/ ^Nm3 30 3 H ₂ ,% 31.4 30.1 O ₂ , % 4.24 0.11 N ₂ ,% 19.9 20.5 CH ₄ ,% 6.49 5.67 CO,% 20.6 24.6 CO ₂ ,% 21.0 22.4 C2,% – 0.23 C3, % – 0.11

It can be seen from Table ₂ that after changing _the carrier gas from _pure N ₂ to simulated gasification gas, the removal rate of tar decreased slightly. The increase in concentration may be due to the fact that a small amount of H ₂ was oxidized to H ₂ O during the partial oxidation reaction of tar, and the partial oxidation reaction of CH ₄ also occurred at the same time, converting CH ₄ into CO and H ₂ .

The method for the dielectric barrier discharge plasma partial oxidation of tar provided by the present invention has been described in detail above. The description of the above embodiments is only used to help understand the technical scheme of the present invention and its core idea. It should be pointed out that for those skilled in the art For those who do not depart from the principle of the present invention, some improvements and modifications can also be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (7)

1. A method for dielectric barrier discharge plasma partial oxidation of tar in crude gas, characterized in that the method comprises the steps of: the crude gas obtained from biomass gasification is dedusted and _O fully mixed in a gas mixer After that, it enters the plasma reactor; the mass ratio of _O2 and tar is controlled to be 1.4 to 1.7; in the plasma reactor, tar, oxygen and gas are partially oxidized at 200-450°C under plasma activation, and the The tar molecules are converted into CO and _H2 combustible gases to realize the purification of gas. 2. The method according to claim 1, characterized in that the temperature in the plasma reactor is 300-350°C. 3. The method according to claim 1, characterized in that, for the raw gas after dedusting, utilize a gas chromatograph to analyze the gas composition, calculate the explosion limit range of the gas; and determine the tar concentration by solvent absorption-weighing method. 4. method according to claim 3, is characterized in that, described solvent absorption-weighing method selects Virahol for use as tar absorption liquid. 5. The method according to claim 1, characterized in that the plasma generation mode in the plasma reactor is dielectric barrier discharge. 6 . The method according to claim 5 , wherein the energy density of the dielectric barrier discharge is 0.1-1.0 kWh/Nm ³ . 7 . The method according to claim 5 , wherein the energy density of the dielectric barrier discharge is 0.6 kWh/Nm ³ .

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