1. bubble saturation method
The coke oven gas from the blower enters the gas preheater after passing through the electric tar catcher. In the preheater, indirect steam is used to heat the gas to a temperature of 60 ~ 70℃ or higher, so that the gas enters the bubble saturator, and the excess water in the saturator is evaporated to keep the water balance in the saturator. The preheated gas enters the saturator along the central gas pipe of the saturator, and bubbles out from the acidic mother liquor through the bubbling umbrella, and the ammonia in the gas is absorbed by sulfuric acid. After leaving the saturator, the gas enters the deacidifier, captures the acid mist it carries, and sends it to the crude benzene section. The ammonia content in the gas behind the bubble saturator is generally less than 0.03g/m3. When pyridine is not generated, ammonia obtained by evaporation of the residual ammonia water in the condensation section directly enters the saturator; When pyridine is generated, ammonia gas is introduced into the pyridine neutralizer. Ammonia reacts with free acid and pyridine sulfate in the mother liquor in the neutralizer to generate ammonium sulfate, which returns to the saturator with the mother liquor refluxed by the neutralizer.
Ammonium sulfate is continuously generated in the mother liquor of the saturator. When the content of ammonium sulfate is higher than its solubility, crystals precipitate and deposit on the bottom of saturator. The crystal at the bottom is pumped into the crystallization tank, where the crystal grows and precipitates at the bottom. Put the ammonium sulfate crystals at the bottom of the crystallization tank into a centrifuge for centrifugal separation, filter out the mother liquor, and wash the crystals with hot water to reduce free acids and impurities on the surface of ammonium sulfate. The mother liquor separated by centrifugation flows back to the saturator together with the mother liquor flowing out of the crystallization tank. The ammonium sulfate crystals separated from the centrifuge are sent to the boiling dryer by the screw conveyor, dried by hot air, sent to the ammonium sulfate storage hopper, weighed and packaged, and then entered the finished product warehouse.
In order to make the gas in the saturator fully contact with the mother liquor, it is necessary to make the bubble umbrella have a certain liquid sealing height in the mother liquor and ensure the liquid level in the saturator to be stable. Therefore, the saturator is also provided with a full-flow port, and the mother liquor overflowing from the full-flow port flows into the full-flow tank through the full-flow tube inserted into the liquid seal to prevent gas from escaping. The lower part of the full-flow tank is connected with a circulating pump, and the mother liquid is continuously pumped into the ejector at the bottom of the saturator. Therefore, the mother liquor in the saturator is continuously circulated and stirred to improve the crystallization process.
The coal tar mist brought by coal gas into the saturator reacts with sulfuric acid in the saturator to generate so-called acid coal tar, and the foamed acid coal tar floats on the surface of the mother liquor and flows into the full-flow tank together with the mother liquor. The acidic coal tar floating on the liquid surface of the full-flow tank should be fished out in time, or introduced into a separation treatment device to be separated from the mother liquor to recover the mother liquor. The sulfuric acid that needs to be replenished in the saturator is transported from the sulfuric acid warehouse to the high tank, and then flows into the saturator. During normal production, the acidity of mother liquor should be kept at 4% ~ 6%, and the amount of sulfuric acid should be the required amount of ammonia. When crude light pyridine is not produced, the amount of sulfuric acid is large, so it is necessary to neutralize the ammonia that enters the saturator with ammonia.
After a certain period of operation, the resistance of the saturator will increase due to the deposition of crystals, which will cause the saturator to block in serious cases. Therefore, pickling and washing must be carried out regularly in the operation. When adding acid regularly, supplementing water, washing saturator and deacidifier, a large amount of mother liquor overflows into mother liquor storage tank. In the normal production process, these mother liquids are pumped back to the saturator for replenishment. Saturator is a kind of equipment that runs periodically and continuously. In order to prevent crystal blockage, acid and water are added regularly to destroy the normal conditions of crystal formation. In addition, the crystal stays at the bottom of the saturator for a short time, so the crystal particles are small with an average diameter of 0.5 mm, which are all shortcomings of the bubble saturator.
2. Spray saturator method
The spray saturator is divided into an upper section and a lower section. The upper part is the absorption chamber and the lower part is the crystallization chamber.
The gas from the desulfurization process is preheated to 60 ~ 70℃ or higher by the gas preheater to keep the water balance of the saturator. After preheating, the gas enters the upper section of the spray saturator and is divided into two streams, which flow circularly along the horizontal direction of the saturator. Each stream of gas is injected into the circulating mother liquor containing 3.5% ~ 4% free acid through several nozzles to absorb the ammonia in the gas, and then the two streams of gas are merged into one stream, which enters the back chamber of the saturator from the mother liquor of the small mother liquor circulating pump (also called secondary spray pump) for secondary spraying to further remove the ammonia in the gas. The gas enters the acid remover in the saturator along the tangential direction, removes acid mist droplets entrained in the gas, leaves the saturator through the upper central outlet pipe, and then the trace acid mist in the gas enters the final cooling benzene washing section after being captured by the mist catcher. The ammonia content in the gas after spraying the saturator is generally less than 0.05g/m3.
The upper and lower sections of the saturator are communicated through a downcomer. The mother liquor after ammonia spraying flows from the concept of falling liquid to the bottom of the crystallization chamber, where the crystal nucleus is pushed up by the saturated mother liquor, and the mother liquor is continuously stirred, so that the crystal nucleus of ammonium sulfate grows up and particles are classified. The slurry at the bottom is pumped to the crystallization tank by crystallization pump. The mother liquor containing small particles rises to the upper part of the crystallization chamber, and the mother liquor circulating pump pumps the mother liquor from the upper part of the crystallization chamber and sends it to two groups of spray boxes at the upper section of the saturator for circular spraying, so that the mother liquor continuously circulates between the upper and lower sections.
The upper section of the saturator is equipped with a full flow tube to keep the liquid level and seal the gas so that the gas cannot enter the lower section. The full-flow pipe inserted into the overflow tank 7 also seals the gas so that the gas cannot escape. The mother liquor overflowed from the overflow port of the saturator flows into the liquid sealing tank in the overflow tank, then overflows into the overflow tank, and then is pumped into the back chamber of the saturator and sprayed together with the small mother liquor. When washing and adding acid, the mother liquor passes through the overflow tank to the mother liquor storage tank, and then is pumped to the saturator with small mother liquor. In addition, the mother liquor storage tank can also be used to store mother liquor when the saturator is overhauled.
Let the slurry in the crystallization tank stand for stratification, and the crystals at the bottom are discharged into the centrifuge. The separated and washed ammonium sulfate crystals are sent to a vibrating fluidized bed dryer by a belt conveyor, dried by air heated by a hot air blower, and then cooled by cold air to enter an ammonium sulfate storage hopper. Then weigh, package and send to the finished product warehouse. The mother liquor filtered by the centrifuge flows back to the lower part of the saturator together with the mother liquor flowing out of the crystallization tank. The dried ammonium sulfate tail gas is discharged into the atmosphere by an exhaust fan after passing through a cyclone separator.
In order to ensure that the circulating mother liquor has a certain acidity, 90% ~ 93% concentrated sulfuric acid is added to the inlet pipe or full-flow pipe of the continuous mother liquor circulating pump to maintain the normal acidity of the mother liquor.
The sulfuric acid sent from the oil depot is sent to the sulfuric acid storage tank, then pumped out by the sulfuric acid pump and sent to the sulfuric acid storage tank, and then flows to the full flow tank by itself.
In the process of producing ammonium sulfate with spray saturator, the spray saturator is made of stainless steel, which has long service life and integrates pickling absorption, crystallization, acid removal and evaporation. It has the characteristics of small gas system resistance, large grain size, average diameter of 0.7mm, good quality of ammonium sulfate, short process flow and simple operation. This process is usually used to recover ammonia from coal gas in newly built and rebuilt coking plants.