Ammonium Sulphate Prodution from Coke oven gas containing Ammonia when reacted with Sulphuric acid

Ammonium Sulphate production from coke oven gas containing ammonia

Coke oven gas with a pressure of 2500 mm WC from exhauster is fed to ASP. Ammonia present in co gas is recovered in ASP as ammonium Sulphate fertilizer. By simple approximation of unit operation the process can be described as follows.

PROCESS:

The co gas from the exhauster is fed to pre-heat the gas to 60-700C. But according to our atmospheric temperature, this temperature is obtained after the exhauster. So the gas is directly fed to the saturator.

SATURATOR:

Saturator is a cylindrical vessel with a conical bottom. It is provided with a bubbler hood, which is duct prolonged to the middle of the saturator. The duct has a hood at the bottom provided with vanes like arrangement. Another ring-like structure with small openings is at the conical portion, which is used for nitrogen feeding. Hot water rings are provided at the top of saturator. Saturator is always maintained with acid bath called liquor, which contains 4-5% of sulphuric acid. The coke oven gas enters through the bubbler hood which is dipped in the bath. The gas rises through the mother liqueur. During this period, the ammonium present in the gas reacts with the sulphuric acid in the liquor. The following reactions will take place in the saturator

NH3 + H2SO4 → NH4 (HSO4)

NH4 (HSO4) + N H3 → (NH4)2SO4

Ammonium Sulphate thus formed settles at the bottom of saturator. Pure nitrogen is purged into the saturator through N2 rings at 6-7 kg/cm2. N2 purging increases crystal growth. Pure Sulphuric acid (98%) is fed to the saturator to maintain the acidity in the saturator. The gas collected at top of the saturator is fed the acid trap. As the gas rises up, some of the crystal may be carried with the gas and they get stacked to walls of the saturator at top. Then the hot water is sprayed to ring provide. The crystal attached to the walls of saturator is washed away. When hot water has sprayed the concentration of the liquor decreases. So inlet acid concentration is increased to 6-7% at that period. After the reaction, the mother liquor is continuously drawn to circulating tank provided at the side of the saturator. This acts as a seal for saturator. From the circulating tank, the mother liquor is fed to the mother liquor tank. The crystals collected at the bottom are fed crystal receiver tank by using a pump

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ACID TRAP:

The outlet of the saturator carries some acid mist. In order to remove the acid Mist, the gas is sent to the acid trap. It is a hollow cylindrical vessel. The coke oven gas from saturator enters tangentially to the trap. Due to the centrifugal motion, the acid mist gets separated. The acid collected a bottom is fed to the circulating tank. The Coke oven gas is fed to the Benzol recovery.

CRYSTAL RECEIVER TANK:

Ammonium slurry from the bottom of the saturator is pumped to crystal receiver tank with conical bottom the ammonium Sulphate crystal settled at the conical portion of the tank, which is wet liquor. The mother liquor from the top of the receiver is fed to the saturator. The slurry from the top of the receiver is fed the saturator. The slurry from the bottom is fed to centrifuge.

DRIER:

Drier is a Design of Fluidized Drier. The principle is based on the loose materials property to acquire fluidity in the air flow under a definite air velocity. The crystal from centrifuge contains some amount of moisture. To remove this moisture crystal are to be dried. The drier is provided with a screen at the bottom, ceramic rings are arranged at the bottom of the screen. The drier is provided with forced draught fan and air, heated in the duct. A spreader at the feed chute of the drier spreads the feed in all directions.

Forced draught fans suck the atmospheric air and feed to the drier. The discharge chute of the fan is divided into two sections. The air is heated to 120 -150 deg C by using the steam and the hot air is feed from the bottom of the screen. The ceramic rings distribute the air in all directions and allow the crystals in a fluidized state. The temperature of the air is sufficient moisture of the crystals. At the discharge end of the drier, cools the crystals.

When the pressure level of the fluidized bed reaches the set point (300-400mm Wc) an automatic discharge feeder discharge the dry ammonium Sulphate to the bucket elevator. The elevator discharges the dry product into the bunker, which in turn feeds the product to the bagging machine. The zone above the fluidized bed is kept under 5-10mmWc in order to avoid the carry-over of the ammonium Sulphate particles out of the drying unit to the dust catcher.

CYCLONE SEPARATOR:

The air from the drier is sucked by the suction fan and feed to the cyclone separators. Cyclone separators separate fine ammonium Sulphate crystals in the air and feed to the bunker. The air from the cyclones is feed to the dust collecting tanks which contains flushing liquor up to certain level. The dust-laden air is then fed to the bottom of the tank. The crystals then dissolved in the water and the air is vented into the atmosphere.

MOTHER LIQUOR TANK:

The excess liquor from the saturator enters the mother liquor tank. Each saturator is provided with two mother liquor tanks. One is vertical and is horizontal. First, the Liquor enters the horizontal tank. As the liquor has less density than the tar it floats. Then the clear mother liquor from the bottom is feed to the vertical tank. From the bottom of the vertical tank, the mother liquor is fed to the saturator through the pumps provided. The concentration of the liquor is maintained at 10-12 %. If the concentration decreases, the density of the liquor decreases and it may be contaminated. Then crystals may become back.

NITROGEN SUPPLY FOR AGITATION

Nitrogen flow to the saturator is normally 450- 550 m3/h, at nitrogen pressure before saturator 0.5- 0.7kg/cm2. For saturator stopping, reduce the nitrogen flow to 100m3/h. once the gas valves are vents unsaturated, stop the nitrogen flow completely.

Coke oven gas is a product of coal coking in C.O. battery its composition is as follows based approximate design of plants.

Hydrogen - 50 - 60;

Methane - 25 -33;

Carbon dioxide - 7-8;

Carbon monoxide - 2.2-3;

Nitrogen - 3-4;

Oxygen - 0.2-0.8;

Unsaturated compounds - 2-2.5

Ammonia vapor - 6-12g/m3;

Hydrogen supplied - 6-12 g/m3

Coke Oven Gas Purification and Cooling Process

The gas collected at gas collecting main from coke oven is cooled by spraying circulating Ammonical liquor. The cooled coke oven gas along with excess liquor enters into the separator. Here the gas and liquor get separated. The coke oven gas from separator comes to the Primary Gas Coolers where the temperature of the gas is reduced from 80 deg C to 30 deg C by means of cooling water.

Primary Gas Cooler:

The coke oven gas from the separator is fed to the PGC from the top. The cooler consists of three zones. This is a shell and tube heat exchanger in which the CO gas exchanges with service water in the top two zones and with chilled water in the bottom zone the tubes are inclined in all the zones. The inclination is maintained at 15°c with the horizontal. This provides any naphthalene condensate to drain easily. The main purpose of PGC is to cool the gas from 90°c to 30°c.

Final Coke Oven Gas Scrubber

During this cooling process, the naphthalene and traces of tar present in the gas condense and this is collected at the bottom of the PGC. The liquid collected at the bottom is sent to the seal pot by gravity. The level in the seal pot should be maintained constant as this acts as a seal to the gas in the cooler.

Tar at a temperature of 90°c is flushed from the top of the cooler to remove the condensed naphthalene on the tubes. The tar is then collected at the bottom of the seal pot. Tar and naphthalene from the seal pot are fed to the storage tank of the CPH. The CO gas from the bottom of the PGC is fed to the electrostatic precipitator.

• Gas temperature before PGC 80-95°c

• Gas temperature after PGC 27-30°c

• Service water inlet temperature 32-33°c

• Service water outlet temperature 43°c

• Gas condensate flow to each PGC 10-15 Nm3/hr

• Chilled water inlet temperature 11-12°c

Electrostatic Precipitator:

The CO gas enters the ESP from the bottom. Electrostatic precipitators are cylindrical vessels with a conical bottom. Each ESP is provided with a seal pot. A round disk having electrodes in suspended state is present inside the precipitator. Electrodes are nothing but SS metal rods. Three are present at the top of the precipitator, which supplies the necessary power to each ESP. the high voltage of about 50,000 volts is supplied to each electrode. Due to high voltage the fine and foggy target slicked to the walls of the electrodes and they fall down due to gravity. The liquid thus collected at the bottom is fed to the seal pot. Each electrode is covered to prevent the connection between any two electrodes.

• Capacity 30,000 Nm3/hr
• Voltage 70KV
• Number of electrodes 148
• ESP insulator boxes temperature 80°C

Final Gas Cooling Plant Process Steps:

• The coke oven gas from the asp plant contains crude benzol and naphthalene and these should be removed from the gas to prevent damage to the pipelines.
• The gas enters the cooler at nearly the middle, it meets the down coming water and the naphthalene present in the gas is almost carried away with it to the bottom.
• The gas along with crude benzol is now cooled to 28-30 deg C in a chiller.It then enters
• The scrubber where the benzol in the gas is absorbed into a (solvent) SOLAR OIL
• The solar can be recovered completely by removal of the crude benzol in it.
• The naphthalene which is carried along with water to the bottom section of the cooler is now treated with TAR so that the naphthalene in the water is absorbed into TAR and both naphthalene and tar can be separated by further treatment

Final Gas Coolers

Final Gas Cooling and scrubbing system

From the saturator, the co-gas enters the acid trap where the acid vapours that might be carried along with the co-gas are separated and sent to saturator .the acid-free vapour of co-gas enters the final gas cooler. There are two final gas coolers at diameter 5m & 45.5m height each cooler has got two sections in the top sections co-gas is sent from the bottom at the top sections and cooled service water is sprayed from the top there is parallel perforated plate aluminum packing of each scrubber which provides the necessary contact time for the water co-gas.

The co-gas enters the final gas coolers min at 55degC cooling of the co-gas is done by direct water spray through a closed cycle system in this way naphthalene that is present in co-gas is scrubbed by water & this enters the bottom of the section. The bottom section naphthalene washer having tar will come in contact with warm water from top sections lighter than tar the water to the top leaves the cooler. During this process whatever naphthalene present in the water will get dissolved in tar because the solubility of naphthalene in tar & many items higher than water than this tar is taken out & stored in tanks and sent to the tar distillation plant for processing.

In this scrubber solar oil is used, as a solvent for scrubbing of benzol from co-gas benzol is dissolved in solar oil from co-gas. Benzol is dissolved in solar oil from benzolised oil it will be sent to the benzol distillation column where solar oil and benzol are separated the separated solar oil will be recycled again to scrubber in this way it is a closed system where 1 ton 70-75kgs of oil is consumed because of losses.

Coal Chemicals Production from Coal Destruction(coke oven gas) Process: Plant Block Diagram

Production of coal chemicals from
coal destruction process:
plant  block diagram

coal a solid fuel used as secondary energy source after petroleum fuels and the origin of coal is approximately explained as the same of the petroleum, organic material subjected to high pressures conditions without the presences of oxygen which made their structure to develop hydrocarbon material as coal, when coal is burned in the presence of air components present in it having long range of boiling points(more volatile compounds and heavy molecular weight compounds) will be combusted at different frequencies leaving the flue gas with a lot of noncombustible compounds.


By chemical analysis we can get lots of chemical structured compounds present in it, trapped in a solid form, unlike liquid petroleum it has to be distilled to extract the fractions, but due to it physical property and moreover plants which produce steel and power plants which generate electricity by the coke which is obtained from coal is used as raw material, not these plants all the chemical industries and heavy machinery plants use coke as energy source instead of coal due the chemical compounds present in it, well for the purpose coal is heated in the absence of air up to 1000 to 1200 degree centigrade and all the compounds except carbon rich coke are collected and purified for the chemical compounds,
In a steel manufacturing industries coal is subjected to destructive distillation in a coke oven, for about nearly 24 hr and the gases are collected for extraction of fractions, it is sequence operation

Coke oven gas: gas which is liberated during coking procedure of coal in a coke oven, which consists of valuable by-products, is called coke oven gas.

Separator: the hot gas is cooled in the collection chamber and about 60 percent of tar is condensed and coal particles which are carried over are flushed with a flushing liquid, at separator the liquid and uncondensed gas are separated.

Primary cooler: gas is cooled to 25 to 30-degree centigrade by indirect contact with water in countercurrent flow.

Electrostatic tar precipitator: ETP is used for removal of tar which is in the form of fog present in the coke oven gas from the primary cooler.

Ammonia absorber: coke oven gas contains 3 percent of ammonia and this is reacted with sulphuric acid to form ammonia sulphate fertilizer.

Benzol recovery: benzene, toluene and xylene are in the form of benzol are recovered in this section leaving out clean coke oven gas which is used a fuel for the plant.