Separation of moisture from coal tar

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Improvements to the tar-ammonia separation system to address clogging issues: The second phase of Tangshan Jiahua Coal Chemical Co., Ltd. features 6.25m rammed coke ovens, with an annual production capacity of 2.2 million tons of coke. The tar-ammonia water separation system uses advanced equipment such as press pumps and super centrifuges to crush and separate the tar residue. The tar intermediate tank has a diameter of DN12500 and a height of 9500; the tar intermediate pump has a flow rate of 22 m3/h and a head of 28 m. The tar separated in the tar-ammonia water separation tank is pumped out using a tar pump and sent to a supercentrifuge for further dehydration and deslagging. After dehydration and deslagging, the tar flows naturally into the intermediate tar tank, and then is pumped to the oil storage facility using a tar pump. Due to the fact that the slag removal equipment in this process is located after the tar-ammonia separation tank, this leads to frequent blockages in the tar outlet at the bottom of the cone-shaped section of the tar-ammonia separation tank as well as in the pipeline leading to the inlet of the intermediate tar pump, thereby severely affecting the continuous and stable operation of the production process as well as the working conditions on site. 1. Process overview: The tar-ammonia mixture from the raw coal gas pipeline enters the tar residue pre-separator. A screen is installed at the outlet of this pre-separator; solids larger than 8 mm settle at the conical bottom of the pre-separator and are removed using a tar pumping pump. In the pressing pump, the solid substances are crushed and sent back to the upper part of the tar residue pre-separator, where they pass through a sieve and enter the tar-ammonia water separation tank. The tar-ammonia mixture leaving the tar residue pre-separator enters the tar-ammonia separation tank, where the separation of tar and ammonia takes place. Due to differences in temperature and density, tar sinks to the bottom. A conical bottom plate is provided at the lower part of the tar-ammonia separation tank to direct the tar toward the tar outlet pipe. The tar is pumped out using a tar intermediate pump and sent to a supercentrifuge for further dewatering and slag removal. The treated tar flows automatically into the tar intermediate tank, from where it is transported to the oil storage facility via a tar pump. The tar residue separated by the super-centrifuge is transported to the coal preparation area using a tar residue truck. 2. Renovation measures: (1) Install a tar circulation pipeline between the tar-ammonia water separation tank and the pre-separator. In the original design, the inlet of the intermediate pump for the two tar streams was connected to the ammonia separation tanks for those tar streams via a pipeline, while its outlet was connected to the supercentrifuge via another pipeline. Due to the prolonged coking time, the tar system is unable to supply tar continuously, which causes tar residues to accumulate continuously at the bottom of the tar-ammonia separation tank, blocking the bottom of the cone in this tank as well as the inlet pipes of the intermediate tar pump. To prevent blockages, a DN125 pipe was added at the inlet of the intermediate tar pump, and two DN80 pipes were added at the outlet, thereby connecting the intermediate tar pump to the pre-separator. Instead of using just one intermediate tar pump to supply oil to the intermediate tar tank intermittently, two such pumps are now used in operation continuously. The tar residue at the bottom of the tar-ammonia separation tank is continuously sent to the pre-separator for recycling, in order to reduce the time that this residue stays at the bottom of the tank. A pressing pump is also used to further crush the tar residue. To ensure sufficient circulation volume and transport capacity, the flow rate of the intermediate tar pump was changed from 22 m3/h to 50 m3/h; as a result of this modification, blockages in the inlet pipeline of the intermediate tar pump were reduced. The renovation schematic is shown in Figure 1. Figure 1: Schematic diagram of the modified circulation pipeline ⑵ New tar discharge pipeline added. To prevent the tar outlet pipe at the bottom of the conical section of the tar-ammonia separation tank from becoming completely blocked and disrupting normal production, there is a DN80mm pipe reserved for the tar overflow bottle along the line parallel to the inclined plates at the bottom of the cone in that tank. Our company uses this pipe to connect it to the existing tar pipeline, serving as a backup pipe for discharging tar. The renovation schematic is shown in Figure 2. Figure 2: Schematic diagram of the spare tar discharge pipe for the separation tank. ⑶ Add two slag scraping tanks. To completely resolve the problems of blockage in the tar-ammonia separation tank and the inlet pipeline of the tar intermediate pump, it is necessary to remove the tar residue before the tar-ammonia separation tank. Our company plans to add two mechanical slag-scraping tanks in front of the tar-ammonia water separation tank. The solid particles larger than 8 mm, which are discharged from the bottom of the pre-separator, are sent to these mechanical slag-scraping tanks using a tar pumping unit. The tar residues settle in these tanks and are then removed, while the tar is sent to the tar-ammonia water separation tank for further separation. The renovation schematic is shown in Figure 3. Figure 3 Schematic diagram of the modification involving the addition of a scum removal trough. 3 Conclusion: The modification completely resolved the problems of blockage in the tar-ammonia water separation tank and the inlet pipe of the tar intermediate pump, ensuring the stable operation of the tar-ammonia water separation system; moreover, the operating conditions on site were greatly improved.