Method of cleaning exhaust gases from the so2and nox

 

(57) Abstract:

The invention can be used for purification of exhaust gases of power plants. Exhaust gases are in contact with coke, obtained by pyrolysis of coal to form pyrolysis gases and exhaust gases prior to contact with the coke pre sequentially heated by utilizing the heat of the cleaned gases due to the combustion of pyrolysis gases, contacting the flue gas with coke is carried out at 750-850oC and a contact time of 0.02-0.45 and with the formation of the activated coke recovered from the SO2sulfur vapor and of NOxnitrogen, and the resulting scrubbed gas serves as a heat carrier to the stage of pyrolysis of coal and after preheating flue gas is cooled with the release of the condensed sulfur. The invention allows the simultaneous clearing of NOxand SO2at one stage. 1 Il.

The invention relates to a method for cleaning exhaust gases from harmful gaseous emissions and can be used for purification of exhaust gases of power plants and other industrial enterprises.

A known method of cleaning exhaust gases from harmful gaseous emissions, e.g. what if 680-710oC with getting restored from SO2sulphur, cooling the purified gas with the Department of sulfur (Japan's Bid N 57 - 190637, B 01 D 53/34, publ. 24.11.82).

The disadvantage of this method is low efficiency of flue gas cleaning, which allows the purification of gases by restoring the carbon only SO2. Nitrogen oxides are practically not restored.

The closest technical solution is the method of cleaning exhaust gases from the SO2and NOxincluding the injection box in the flow of exhaust gases ammonia and contacting this stream at a temperature of more than 70oC with activated carbon containing catalytic additives, with the adsorption of SO2on the surface of activated carbon and restoration of NOxto nitrogen (Japan's Bid N 55-81728, B 01 D 53/34, publ. 20.06.80).

The disadvantage of this method is that in the known process is used as the reducing toxic NH3and when operating it possible leakage of unreacted NH3and release it into the atmosphere. In addition, the use of expensive catalysts requires additional costs and increases the cost of the entire treatment process. In the famous pic is of subramania is to increase the efficiency of the method by combining the process of purification of exhaust gases from the SO2and NOxwith the simultaneous production of activated coke and more efficient use of the internal heat of the whole process.

This object is achieved in that the coal is subjected to pyrolysis with the formation of pyrolysis gases and coke, exhaust gases pre sequentially heated due to the utilized heat treated gases due to the combustion of pyrolysis gases and serves to contact Cox at 750-850oC and contact time of 0.02-0.45 and with the formation of the activated coke and restored from SO2sulfur vapor and of NOxnitrogen, purified gas is sent as a coolant to the stage of pyrolysis and then preheating the exhaust gases with subsequent cooling of the cleaned gases and the release of the condensed sulfur.

When the temperature decreases recovery below 750oC there is a significant difference in the values of the reaction rate recovery SO2and NOxcarbon, which makes the joint cleaned off-gases from these contaminants. In addition, there is a sharp decrease in the efficiency of concurrent treatment, while maintaining a given treatment efficiency increases contact time othodoxy recovery above 850oC requires an additional external supply of heat to the heat produced inside the process, which greatly impairs the efficiency of the process.

When values of the contact time of the exhaust gases from the coke layer below the declared area decreases the effectiveness of their simultaneous cleaning from the NOxand SO2.

When values of the contact time of the exhaust gases from the coke layer above the declared area increases the size of the machine without substantially increasing the efficiency of treatment.

The drawing shows a diagram of the device carrying out the claimed method.

Device for cleaning exhaust gases contains Pyrolyzer 1, the reactor, the reducing agent 2, heater 3, the combustion chamber 4, a capacitor 5.

Method of cleaning exhaust gases is carried out as follows. Dry coal fraction 5-50 mm served in Pyrolyzer 1. The pyrolysis of the coal occurs at a temperature of 650-750oC. the coke formed in the pyrolysis process, enters the reactor, the reducing agent 2 at a temperature of 750-850oC is the restoration of NOxand SO2and activation of coke as a result of interaction with CO2and water vapor contained in the exhaust gas. Contaminated on the 2. In the combustion chamber 4 is the combustion of pyrolysis products coming from Pyrolyzer 1, with formation of gaseous coolant. The cleaned flue gases from the reactor-reducing agent 2 can be Pyrolyzer 1 as the coolant, then served in the heater 3 for heating the contaminated exhaust gases. Next, the partially cooled purified exhaust gases are transferred in the condenser 5, where pairs condense sulfur, and sulfur is removed in liquid form, and the purified exhaust gases are directed into the chimney.

The efficiency of purification of exhaust gases from the NOxand SO2depends on the time of contact with the layer of coke and temperature in the reactor, the reducing agent 2.

In the present method combined two processes: purification of exhaust gases from the NOxand SO2and the production of activated coke. The combination of these processes occurs in the reactor, the reducing agent 2, where exhaust gas cleaning is the activation of coke obtained in the pyrolysis of coal. The cleaned flue gases are used as carrier of the pyrolysis of coal. For heating the contaminated exhaust gases is used heat treated exhaust gases, disposal of which is going to implement the processes of purification of exhaust gases from the NOxand SO2and produce an activated coke is not happening.

Experimentally investigated the kinetics of the reactions of NOxand SO2with coxae obtained by the pyrolysis of lignite and coal. In the result of the interaction of NOxand SO2with coxae at elevated temperatures occur following reaction recovery:

C + 2NO2- 2NO + CO2(1)

C + 2NO - N2+ CO2(2)

C + SO2- S + CO2(3)

Oxrestored to molecular nitrogen,

O2restored to elemental sulfur. Reaction (1), (2) and (3) are first-order reactions. The studies were conducted in the temperature range of 350-900oC.

As a result of experiments determined values of the rate constants of the reactions of NO recovery and SO2carbon chars studied.

The optimal temperature range for simultaneous (one-step) NO recovery and SO2is the temperature range 750-850oC, where the rate of reactions (2) and (3) are approximately equal. The rate of reaction (1) is much higher than the rate of reaction (2). In the temperature range of 750-850oC when the values of time of contact of the exhaust gases from the coke layer of 0.02-1 with NO2output

When the temperature drops below 750oC is the difference in the speeds of the reactions of NO recovery and SO2carbon, which makes the simultaneous purification of exhaust gases from these contaminants. In addition, there is a sharp decrease in the efficiency of concurrent treatment, while maintaining maximum efficiency of purification increases the contact time of the exhaust gases with a layer of coke, and, consequently, increase the size of the installation.

The temperature increase recovery above 850oC requires an additional supply of heat to the heat produced inside the process.

The values of contact time of the exhaust gases from the coke layer in this region correspond to the efficiency of the simultaneous cleaning from the NOxand SO280 to 99.9%.

When values of the contact time of the exhaust gases from the coke layer below the declared area decreases the effectiveness of their simultaneous cleaning from NO and SO2.

When values of the contact time of the exhaust gases from the coke layer above the declared area increases the size of the machine without substantially increasing the efficiency of treatment.

EXAMPLES

Exhaust gases containing % collection: CO2- 12 the coal with a particle size up to 50 mm served on pyrolysis in the temperature range 650-750oC.

The resulting pyrolysis coke with a particle size up to 30 mm) is fed into the reactor, the reducing agent 2.

EXAMPLE 1

The temperature in the reactor is the reducing agent 750oC.

The contact time of the exhaust gases with a layer of coke is installed 0,075 C.

The rate constants of the reaction of NO and SO2at a temperature of 750oC is:

- coke of lignite:

KNO= 39,56 with-1;

= 21,55 with-1.

The degree of purification will be for NO - 94,8%, for NO2~ 100%, SO2- 80,1%.

- coke of coal:

KNO= 34,20 with-1< / BR>
= 21,57 with-1< / BR>
The degree of purification will be for NO - 92,3%, for NO2~ 100%, SO2- 80.2 per cent.

EXAMPLE 2

The temperature in the reactor is the reducing agent 800oC.

The contact time of the exhaust gases with a layer of coke is installed 0,050 C.

Contacts the reaction rates of NO and SO2at a temperature of 800obe;

- coke of lignite:

KNO- 51,28 with-1< / BR>
= 33,55 c-1< / BR>
The degree of purification will be for NO - 92,3%, for NO2~100%, SO2- 80.3% of

- coke of coal:

KNO= 56,18 with-1< / BR>
= 39,27 with-1< / BR>
The degree clear what sanovitae 850oC.

The contact time of the exhaust gases with a layer of coke is installed 0,030 C.

The rate constants of the reaction of NO and SO2at a temperature of 850oC is:

- coke of lignite:

KNO= 64,97%-1< / BR>
= 53,61 with-1< / BR>
The degree of purification will be for NO - 85,8%, for NO2~100%, SO2- 80,1%.

- coke of coal:

KNO= 88,32 with-1< / BR>
= 67,76 with-1< / BR>
The degree of purification will NO = 92.9% of that for NO2~100%, SO2- 86,3%.

EXAMPLE 4

The temperature in the reactor is the reducing agent 750oC.

The contact time of the exhaust gases from the coke layer is set to 0.17 with.

The rate constants of the reaction of NO and SO2at a temperature of 750oC is:

for coke brown coal

KNO= 39,56 with-1< / BR>
= 21,55 with-1< / BR>
The degree of purification will be for NO - 99,9%, for NO2~100%, SO2of 97.4%.

- coke of coal

KNO= 34,20 with-1< / BR>
= 21,57 with-1< / BR>
The degree of purification will be for NO - 99,7%, NO2~100%, SO2of 97.4%.

EXAMPLE 5

The temperature in the reactor is the reducing agent 800oC.

The contact time of the exhaust gases from the coke layer of the mouth of the BR>
for coke brown coal

KNO= 51,28 with-1< / BR>
= 33,55 c-1< / BR>
The degree of purification will be for NO - 99,8%, for NO2~100%, SO2-98,2%.

- coke of coal:

KNO= 56,18 with-1< / BR>
= 39,27 c-1< / BR>
The degree of purification will be for NO - 99,9%, for NO2~100%, SO2-99,1%.

EXAMPLE 6

The temperature in the reactor is the reducing agent 850oC.

The contact time of the exhaust gases with a layer of coke is installed 0,078 C.

The rate constants of reactions of NO and SO2at a temperature of 850oC is:

- coke of lignite:

KNO= 64,97 with-1< / BR>
= 53,61 with-1< / BR>
The degree of purification will be: for NO - 99,4%, for NO2~100%, SO2- 98,5%.

- coke of coal:

KNO= 88,32 with-1< / BR>
= 67,76 with-1< / BR>
The degree of purification will be: for NO - 99,9%, for NO2~100%, SO2- 98,9%.

Thus, the proposed method of cleaning exhaust gases allows the simultaneous clearing of NOxand SO2in one stage with a high cleaning efficiency from 80 to 99.9%.

This method is highly effective because it combined two processes: purification of exhaust gases from NO and SO

Method of cleaning exhaust gases from the SO2and NOxcomprising contacting the exhaust gas with the reducing agent at elevated temperature with getting recovered from the NOxnitrogen and allocation of purified gas, wherein in use as a reducing agent coke, obtained by pyrolysis of coal to form pyrolysis gases, exhaust gases prior to contact with the coke pre sequentially heated by utilizing the heat of the cleaned gases due to the combustion of pyrolysis gases, contacting the flue gas with coke is carried out at 750-850oC and contact time of 0.02-0.45 and with the formation of the activated coke and restored from SO2sulfur vapor, and the resulting scrubbed gas serves as a heat carrier to the stage of pyrolysis of coal and after preheating flue gas is cooled with the release of the condensed sulfur.

 

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