Coking product recovery process

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1. Condensation and blower section 1) Process flow: Raw gas at -82°C from the coke oven, along with tar and ammonia water, flows through the coal suction pipeline to the gas-liquid separator. After gas-liquid separation, the raw gas exits from the upper part and enters a horizontally arranged primary cooler that operates in parallel, where it is cooled in three stages. The gas is cooled to 21–22°C using 65°C circulating water after the desulfurization section reboiler in the upper section, 33°C circulating water in the middle section, and 16°C cold water in the lower section. The gas discharged from the lower part of the horizontal tube initial cooler enters the electrostatic tar catcher to remove the tar contained in the gas, and is then pumped by a gas blower to the ammonium sulfate production section. The excess heat water from the upper section is pressurized by a hot water pump, exchanged heat with the upper section of the cross-tube pre-cooler, and then sent to the desulfurization unit for reuse. To ensure the cooling efficiency of the primary cooler, a mixture of tar and ammonia water is continuously sprayed in the middle and lower sections, while the top section is periodically rinsed with hot ammonia water to remove impurities such as tar and naphthalene from the tube walls. There is a break tower disk between the middle and lower sections of the primary cooler. The condensate discharged from the upper and middle sections flows into the upper condensate tank through the water seal tank. Part of this condensate is sent to the middle section of the primary cooler using the upper condensate pump, while the excess is sent to the tar residue pre-separator. The condensed liquid discharged from the lower section flows into the lower condensate tank through the water seal groove, and is pumped by a pump in the lower section to be sprayed in the lower part of the primary cooler; the excess amount flows into the upper condensate tank via the transfer pipe. The tar and ammonia water separated by the gas-liquid separator first enter the tar residue pre-separator, where separation of tar, ammonia water, and tar residue takes place. A grating is installed at the outlet of the tar residue pre-separator; solids larger than 8 mm remain in the pre-separator, settle on its conical bottom, and are removed using a tar pumping pump. In the tar pressing pump, solid substances are crushed and sent back to the upper part of the tar residue pre-separator. The filter screen of the tar residue pre-separator is an automatic screening device; if the sieve pores become clogged, they can be cleaned using steam back-purging. The tar-ammonia solution coming out of the tar residue pre-separator enters the tar-ammonia separation tank, where ammonia and tar are separated. At the bottom of the tar-ammonia water separation tank, there is a conical bottom plate; due to differences in temperature and specific gravity, the tar settles at the bottom and is pumped out using a tar intermediate pump and sent to a supercentrifuge for further dehydration and slag removal. The treated tar flows naturally into the tar tank and is then transported to the tar storage area via a tar pump. The ammonia water from the upper part of the tar-ammonia water separation tank flows into the lower circulating ammonia water intermediate tank, from where it is pumped by a circulating ammonia water pump to the coke oven gas collection pipes for circulating and cooling the gas. The remaining ammonia water flows by gravity from the tar-ammonia separation tank to the intermediate tank for remaining ammonia water, where heavy oils are separated through sedimentation; after that, it passes through a tar remover to have the tar removed, and then flows back into the remaining ammonia water tank. From there, it is pumped by a remaining ammonia water pump to the ammonia vaporization unit in the ammonium sulfate production section. The tar-ammonia mixture, which contains about 30–50% tar, is taken out at the interface of the tar-ammonia separation tank and flows by gravity to the lower condensate tank. The tar residue separated by the super centrifuge is discharged into tar residue trucks and sent for coal preparation on a regular basis. 2) Process characteristics: a) The primary cooler uses high-efficiency cross-tube coolers to cool the gas to 21–22°C. A mixture of tar and ammonia water is sprayed in stages within the primary cooler, allowing most of the naphthalene in the gas to be removed through cooling, thereby achieving the goals of cooling, deoiling, and removing naphthalene from the gas and ensuring that subsequent equipment is not clogged. b) The cross-tube coolers are equipped with interstage baffles, which helps reduce the amount of low-temperature water required and lowers operating costs. The excess heat from the upper section is used, after heat exchange, to heat the reboiler in the desulfurization unit, thereby saving steam consumption. c) By using efficient electrostatic tar collectors, the tar content in the gas after treatment can be kept below 50 mg/m3, which facilitates the proper operation of subsequent equipment. Ceramic insulators are filled with nitrogen for protection, reducing the need for maintenance and extending their lifespan. d) The remaining ammonia water has its tar content further reduced through flotation in a tar remover, which prevents the polymerization of tar on the trays of the ammonia evaporation tower, ensures stable operation of the tower, maintains a consistent quality of the ammonia evaporation wastewater, and contributes to environmental protection. 1.1.4.2 Ammonium sulfide section 1) Process flow: The gas coming from the condensation and blower section enters a spray-type ammonium sulfide saturator. In the upper section of the saturator, the gas enters the annular chamber in two streams, where it comes into countercurrent contact with the circulating mother liquor; the ammonia present in the gas is absorbed by the sulfuric acid in the mother liquor, resulting in the formation of ammonium sulfate. The deammoniated gas converges into one stream in the rear chamber of the saturator; after being continuously sprayed and washed by the mother liquor pumped by the small mother liquor circulation pump, it enters the cyclone acid remover in the saturator in a tangential direction. There, the acid mist contained in the gas is separated, and the resulting gas is sent to the final cooling and benzene washing section. The mother liquor located in the upper part of the lower section of the saturator is continuously pumped out by a large mother liquor circulation pump and sent to the annular spraying chamber in the upper section of the saturator for cyclic spraying; the sprayed circulating mother liquor then flows down to the lower section of the saturator through the central downcomer. In the lower section of the saturator, nuclei move upward through the saturated medium, causing the crystals to grow and leading to grain size grading. When the crystal ratio in the ammonium sulfate mother liquor in the lower section of the saturator reaches 25%-40% (v%), a crystallization pump is used to transfer the slurry at its bottom to the indoor crystallization tank. The mother liquor that overflows from the full-flow outlet of the saturator flows by gravity to the full-flow tank, and then is continuously pumped by a small mother liquor circulation pump to the rear chamber of the saturator for cyclic spraying, in order to further remove ammonia from the gas. During the regular flushing of the saturator with acid and water, excess mother liquor flows into the mother liquor storage tank via the full-flow channel ； After rinsing with acid and water, it is gradually pumped out using a small mother liquor circulation pump and replenished to the saturator system. When there is a water imbalance in the saturator mother liquor system (excess water), the mother liquor can be heated using a mother liquor heater, thereby removing the excess water from the gas system and maintaining equilibrium in the system. The ammonium sulfide crystals in the crystallization tank are discharged and separated by centrifugation in an ammonium sulfide centrifuge. The ammonium sulfate crystals separated from the centrifuge are first discharged into a screw conveyor via chutes, and then transported by that screw conveyor to a vibrating fluidized bed dryer; after drying and cooling, they enter the ammonium sulfate storage bin. After weighing and packaging, it is sent to the finished goods warehouse. The mother liquor filtered by the centrifuge, along with the mother liquor flowing out of the crystallization tank in full flow, flows back to the lower section of the saturator by gravity. The exhaust gas exiting the vibratory fluidized bed dryer undergoes two stages of dust removal before being released into the atmosphere. First, most of the ammonium sulfate dust contained in the exhaust gas is removed using two sets of dry cyclone dust collectors. The exhaust gas is then pumped to an exhaust gas cleaning tower, where it is continuously sprayed with recycled mother liquor to further remove any remaining ammonium sulfate dust. Finally, the liquid droplets present in the exhaust gas are removed using a mist separator before the gas is released into the atmosphere. The recycled mother liquor discharged from the exhaust cleaning tower is pumped by the exhaust cleaning tower pump to the top of the tower for cyclic spraying ； At the same time, a small amount of industrial fresh water is continuously and quantitatively added to the exhaust gas scrubbing tower, while the excess mother liquor is sent back to the ammonium sulfate mother liquor system via the full-flow pipe. The 93% concentrated sulfuric acid required for the ammonium sulfate production section is delivered regularly from the acid and base storage area. Concentrated sulfuric acid is first sent to the sulfuric acid storage tank, and then flows by gravity to the full-flow tank of the saturator system. The remaining ammonia water sent from the condensation and blower section, after exchanging heat with the ammonia vapor wastewater discharged from the bottom of the ammonia vaporization tower, enters the ammonia vaporization tower. Direct steam is used to vaporize the ammonia, while the alkaline-containing condensate discharged from the upper part of the desulfurization tower enters the upper section of the ammonia vaporization tower to decompose the fixed ammonia in the remaining ammonia water. The ammonia vapor at the top of the ammonia vaporization tower is condensed using an ammonia condenser before being sent to the saturator. After heat exchange with the ammonia vaporization wastewater and the remaining ammonia solution, it is cooled in a wastewater cooler before being sent to the phenol-cyanide wastewater treatment plant. The asphalt produced at the bottom of the ammonia vaporization tower is regularly discharged into an asphalt pit; after cooling, it is manually removed and taken to the coal yard to be mixed into the coal blend. 2) Process characteristics: a) A spray-type saturator is used, made of stainless steel and thus having a long service life; it combines acid washing, acid removal, and crystallization in one unit. The gas system experiences low resistance, the ammonium sulfate particles are large in size, the process is simple, and the technology is advanced and reliable. b) The equipment and pipelines in the ammonium sulfate mother liquor system are made of ultra-low carbon stainless steel, which ensures a long service life, permits the plant to operate continuously and stably over time, and reduces maintenance costs. c) Vibrating fluidized bed is used for ammonium sulfate drying, which offers good drying efficiency and is easy to operate and maintain. d) The dried ammonium sulfate exhaust gas is subjected to two-stage dust removal using dry and wet methods, resulting in high dust removal efficiency and excellent environmental protection effects. d) The ammonia vaporization tower is a stainless steel floating valve tower, featuring high distillation efficiency, good corrosion resistance, and stable operation. e) Ammonia evaporation combined with alkaline decomposition is used to remove fixed ammonium, reducing the total ammonia content in the wastewater and creating favorable conditions for subsequent wastewater treatment. 3 Final Cooling and Benzene Washing Unit 1) Process flow: The gas at ~55°C from the ammonium sulfate unit enters from the top of the gas final cooler. The final cooler uses indirect cooling and is divided into two stages. The upper section uses circulating water at 33°C, while the lower section employs cold water at 16°C to cool the gas to around –25°C before it enters the benzene washing tower. After the gas has had its crude benzene removed through oil-poor washing, it is sent to the desulfurization unit. To ensure the cooling efficiency of the final cooler, circulating liquid is sprayed continuously in the middle and lower sections, while the excess coal gas condensate is sent to the tar residue pre-separator in the condensing and blasting section. The lean oil sent from the crude benzene distillation section is sprayed from the top of the benzene washing tower, where it comes into contact with the gas in the reverse direction to absorb the benzene present in the gas. The rich oil at the bottom of the tower is pumped by a rich oil pump to the crude benzene distillation section for benzene removal before being reused. 2) Process characteristics a) The benzene washing tower uses lightweight ceramic packing, which has a large specific surface area, reduces investment costs, and offers a long service life. 4 Desulfurization Section 1) The process flow involves gas coming from the benzene washing tower entering the desulfurization tower. The desulfurization tower is divided into two sections: the upper section is the alkali washing section, the lower section is the washing section, with a partition plate located in between. The gas comes into countercurrent contact with the alkaline solution (potassium) from bottom to top, and acidic gases such as H2S and HCN in the gas are absorbed. At the same time, the alkaline solution (NaOH) required to decompose the remaining ammonia and fix ammonium is added to the upper section of the desulfurization tower, thereby further removing H2S from the gas and ensuring that its concentration remains at ≤100 mg/m3. Part of the desulfurized gas is sent back to the coke oven and the crude benzene tubular furnace for heating, while the rest is delivered to customers. The rich liquid that has absorbed acidic gases is divided into two streams, which exchange heat with the hot lean liquid coming from the bottom of the regeneration tower and the hot semi-lean liquid coming from the middle of the tower, before entering the regeneration tower at the top for regeneration. The regeneration tower operates under vacuum and low temperature; the rich liquid comes into contact with the water vapor rising from the bottom of the tower, causing the acidic components to be desorbed. The acidic gas emerging from the top of the regeneration tower enters a condensation cooler, where water is removed from it, after which the acidic gas is sent to the sulfur recovery unit via a vacuum pump. The heat source for the regeneration of the regenerator comes from the waste heat water in the upper section of the primary cooler and 0.15 MPa steam from the waste heat boiler of the Claus unit. The regenerated hot lean liquid and hot semi-lean liquid, after heat exchange with the rich liquid and cooling in a cooler, enter the desulfurization tower from the top and middle of the washing section for reuse. The desulfurization waste liquid is sent to the residual ammonia tank. The acid vapor delivered by the vacuum pump (containing H2S, HCN, and small amounts of NH3 and CO2) enters the Claus furnace. In the burner at the front of the Claus furnace, one-third of the H2S in the acid vapor burns with air to produce SO2, while the remaining two-thirds of the H2S reacts with the resulting SO2 to form elemental sulfur. Its main reactions are as follows: H2S + 3/2O2 → SO2 + H2O; 2H2S + SO2 → 3/2S2 + 2H2O. Nitrides such as NH3, CO2, and HCN in the acidic gas react and decompose into H2, N2, and CO under a high-temperature reducing atmosphere and in the presence of a catalyst. The hydrocarbon compounds in acidic vapors can also be completely decomposed or burned. The high temperature in the furnace is mainly maintained by the heat from chemical reactions. Since the H2S content in the acidic gas is between 50% and 60%, some steam still needs to be introduced to cool the furnace; gas is only used during the startup phase. The high-temperature process gas discharged from the Claus furnace is cooled by a process gas cooler in the waste heat boiler, resulting in the condensation of some liquid sulfur. The process gas discharged from the waste heat boiler still contains H2S and SO2, so it is continuously fed into the Claus reactor to further ensure complete reaction of H2S and SO2. And liquid sulfur is condensed by a sulfur condenser installed in the waste heat boiler and separated by a separator. The heat recovered by the waste heat boiler is used to produce water vapor at 0.15 MPa, which can be employed for heating the tar storage tank and the steam jackets of the tar pipes. The liquid sulfur condensed from the process gas cooler, as well as that separated from the separator, is collected in the liquid sulfur storage tank through a sulfur seal tank. Periodically, it is pumped out and sent to a sulfur granulation machine to produce solid sulfur, which is then bagged, weighed, and exported. To meet the requirements for the inlet temperature of the Claus reactor, part of the hot process gas discharged from the Claus furnace is mixed with the cooled process gas. The flow rate of the hot process gas is controlled by the central tube of the process gas cooler. The process gas discharged from the sulfur condenser in the waste heat boiler, after having the entrained liquid sulfur separated out in a separator, is known as Claus off-gas; it has a temperature of around 135°C and enters the coal-inlet pipeline prior to the gas-liquid separator. The soft water required for the waste heat boiler is supplied from outside; it first enters the boiler water treatment tank, where it is heated by direct steam to carry out steam stripping for degassing. To ensure that the boiler water meets the standards, chemical reagents are added to the water using a reagent pump. The treated soft water is pumped out and enters the waste heat boiler. The air and gas required for the Claus furnace are supplied by an air blower and a gas booster. The Claus furnace is equipped with a flame monitor and a safety shutdown mechanism; in the event of abnormal conditions such as the presence of acid vapor, insufficient air flow, too low pressures of gas or air, or an excessively low boiler liquid level, the furnace will shut down automatically, and the acid vapor is directed to the gas pipeline before primary cooling. Considering that the sulfur production units using the Claus process require regular maintenance, as well as the need to continue desulfurization without shutting down the system, this design includes two sets of sulfur production units. 2) Process characteristics a) Only KOH is used as the desulfurizing agent, resulting in low costs and simple operation. b) The regeneration of the rich liquid is carried out using vacuum distillation; the operating temperature is low, and due to the low oxygen content in the system, side reactions occur slowly, resulting in very little waste liquid being generated. c) The heat source for liquid-rich regeneration is the waste heat from initial cooling, enabling effective utilization of the waste heat from raw gas and thus saving energy. d) The regeneration temperature is low, corrosion is minimal; the absorber, regenerator, and most of the equipment are made of carbon steel, resulting in lower investment costs. e) The sulfur recovery employs a single-stage Claus reaction process, with a conversion rate of H2S of approximately 90%, and the purity of the resulting solid sulfur reaches as high as 99.5%. f) Combining the process gas cooler and sulfur condenser within the waste heat boiler reduces the number of equipment units and the space required. g) A waste heat boiler is installed to make maximum use of the waste heat from the process gas, thereby saving energy and improving the thermal efficiency of the entire system. h) It can completely decompose or burn NH3, HCN, and hydrocarbon compounds in the acid vapor, thereby preventing the effects of ammonium salts and carbon deposits on the catalyst. i) The Claus off-gases are returned to the coal gas absorption pipeline, thus not polluting the atmosphere; the remaining H2S in the off-gases can be recovered further, and the combustible components can also be utilized. 5 Crude benzene distillation section 1) Process flow: The rich oil sent from the final cooling and benzene washing section is sequentially fed through the oil-gas heat exchanger, the second-stage rich-poor oil heat exchanger, and the first-stage rich-poor oil heat exchanger. After being heated to 185–190°C in a tubular furnace, it enters the benzene removal tower, where it is stripped and distilled using direct steam from the regenerator. The light benzene vapor escaping from the tower is cooled by an oil-gas heat exchanger and a light benzene condenser, before entering the oil-water separator. The separated light benzene flows into the light benzene reflux tank; part of it is pumped to the top of the tower using a light benzene reflux pump as reflux, while the rest goes into the light benzene intermediate tank, from where it is then pumped to the refined benzene storage area using a light benzene product pump. The hot lean oil discharged from the bottom of the benzene removal tower is pumped, at a rate of 1–1.5%, into the regenerator, where it is regenerated by steam that has been heated in a tubular furnace. The regenerated residue is discharged into the residue oil tank. The remaining hot lean oil is cooled to ~27°C through the first lean-rich oil heat exchanger, the second lean-rich oil heat exchanger, the first lean oil cooler, and the second lean oil cooler, before being sent to the final cooling and benzene washing section. At the top of the benzene removal tower, there is a break tray as well as an oil-water separator outside the tower, which are used to remove water accumulated at the top of the tower and to ensure stable operation. The refined heavy benzene drawn from the side line of the debenzing tower flows into the refined heavy benzene tank and then by gravity to the refined benzene storage area. The naphthalene oil fraction is taken from the side stream of the debenzing tower to reduce the naphthalene content in the lean oil. The obtained naphthalene oil fraction is sent to the residue oil tank, and periodically pumped to the tar tank in the condensation and blower section. The separated water discharged from each oil-water separator is directed to the separated water tank via control valves, and then pumped to the condensation and blower section. The newly washed oil delivered from the tar storage area enters the washing tank and is supplied to the system via the inlet of the rich oil pump. The non-condensable gases from each storage tank are collected and led into the gas pipeline in front of the blower. 2) Process characteristics: a) A break plate is installed in the upper section of the benzene removal tower to prevent water accumulation on the trays, thereby facilitating the operation of the tower. b) The benzene removal tower has 55 trays and is used to produce two types of benzene. Reflux is provided at the tower top, with side streams for pure benzene and naphthalene; the process is short and requires less investment. c) The exhaust gases from each tank are all introduced into the gas pipeline before the blower, which is beneficial for environmental protection.