45B – Multi-factor cyclone parent-child separator as a solution to eliminate tar and asphalt dust clogging in projects for upgrading low-rank coal into gas
Thread Content
This post was last edited by luoli519 on 2023-10-3 at 12:29. A well-known company took the lead in carrying out the construction and operation of a demonstration facility for upgrading low-grade coal to ** grade. Good progress has been made in the coal tar hydrogenation section. However, in the purification stage of gas produced from low-grade coal upgrading, there are significant operational difficulties in continuously and stably obtaining high-quality coal tar and hydrogen. This is mainly manifested in the rapid clogging of the primary separator during the initial purification of coal-tar-containing, dusty coke oven gas, which causes a \"blockage\" in the pre-separation step for the upgraded gas and prevents the continuous and stable operation of the production process. Improving quality bypasses the \"obstruction\" step, but this results in a large amount of dust reaching the wash tower, thereby causing blockages and obstructions in that tower. Please share your experience with the operation of your own gasification units and participate in the discussion to find solutions.
The purification process for upgrading the gas in this device is simply described as follows: the high-temperature, dust-containing oil and gas produced by coal carbonization has most of its dust removed by a primary separator; after that, further dust removal is carried out by a secondary separator, and then the gas enters a water washing tower. As dust enters the scrubber along with oil and gas, it causes the subsequent scrubbers to become clogged and unable to operate for extended periods of time.
The device was designed by a company in East China. For the initial separation of gas and liquid, a filter-type separation unit was used. Although a backup unit was installed, the filters in this separation unit became clogged very quickly; their lifespan was short, requiring frequent maintenance and replacement. This led to high operational costs, and it was not possible to achieve the technical and economic benefits desired for the project.
The operating parameters for this separation stage are as follows: 1. Operating temperature: 550~560℃； 2. Operating pressure: Operating pressure: -1~1 KPa (G) ； 3. Gas flow rate under operating conditions: 7600 m3/h under normal conditions, up to 8000 m3/h under maximum operating conditions ； 4. Improve the dust content in the gas: ~100g/m3 ； 5. Composition of the gas mixture: Main components of high-temperature oil and gas (Vol%): H2O, 41% ； Tar vapor, 5% ； Gas, 54%. Hydrogen sulfide content: 5600 ppm, ammonia content: 700 ppm.
This post was last edited by luoli519 on 2016-11-2 at 22:08. The filter-type separation unit originally used in the design for dust and tar vapor separation under these conditions for gas upgrading became clogged too quickly, preventing it from operating continuously properly. The owner found a standard-type cyclone separator used in petrochemical industries at a certain university, to replace the original filter-element-based separation system.
After being put into use, this type of separator similar to a standard cyclone separator has shown a significant improvement in terms of continuous operation compared to the original filter element-based filtration separator, and it has been able to operate continuously for over a week. However, it was subsequently found that the tar asphalt dust accumulated and grew significantly near the gas-phase inlet and at the gas-phase outlet, becoming larger and larger, which severely disrupted the flow field and even blocked the inlets and outlets. After half a month of operation, it was stopped again. Fortunately, no more expensive filter elements had to be used.
Since the quasi-standard cyclone separator also became clogged, the owner added a spare quasi-standard cyclone separator following the original designer’s approach, so as to switch to using it. After all, the regeneration of standard cyclone separators does not require spare parts such as filter elements, which represents an improvement over the conventional filter-element-based filtration separators.
The problem actually lies in the oil content. Regarding the purification of this gaseous medium, the practices used in Lurgi or Svedala reactors should be adopted. It can be said that their operating conditions are quite similar.
It is certainly very difficult to use high-efficiency filters for purifying dust- and oil-containing gases in this application.
However, dealing with coking in a quasi-standard cyclone separator is also no easy task. Due to the high-temperature asphalt tar mixed with dust, it cements around the inlet and outlet of the cyclone separator, becoming very hard. It does not fall off after being heated in a solvent for several hours, and high-temperature steam cleaning is also ineffective. It was necessary to use high-pressure air hammers and tightening devices to break it down bit by bit; it took several days to basically remove the caked deposits.
A major criticism of the purification of crude gas in Luchi furnaces is the large amount of wastewater generated. To avoid environmental pressures caused by excessive wastewater volumes, the owners and designers initially considered using dry purification methods as much as possible, minimizing the use of wet methods, and reducing the generation of coking wastewater. The company is located in the northwest, where water resources are scarce; it faces dual pressures regarding water extraction and environmental protection.